diff --git a/modules/misc/news.nix b/modules/misc/news.nix
index 27b1a5f7d..708fd7f6f 100644
--- a/modules/misc/news.nix
+++ b/modules/misc/news.nix
@@ -2029,6 +2029,23 @@ in
           A new module is available: 'programs.foot'.
         '';
       }
+
+      {
+        time = "2021-04-13T07:19:36+00:00";
+        message = ''
+          mbsync channels no longer accepts the masterPattern or slavePattern
+          attribute keys. This is due to an upstream change.
+          They have been renamed: masterPattern -> farPattern, and
+          slavePattern -> nearPattern.
+          This is a stateful change, where the database file(s) used to keep track
+          of mail are silently upgraded once you upgrade both your configuration file
+          and the mbsync program.
+
+          Note that this change is non-reversible, meaning once you choose to switch to
+          near/farPattern, you can no longer use your previous slave/masterPattern
+          configuration file.
+        '';
+      }
     ];
   };
 }
diff --git a/modules/programs/mbsync-accounts.nix b/modules/programs/mbsync-accounts.nix
index cdd5997f1..3f3f2d14d 100644
--- a/modules/programs/mbsync-accounts.nix
+++ b/modules/programs/mbsync-accounts.nix
@@ -50,13 +50,13 @@ let
         '';
       };
 
-      masterPattern = mkOption {
+      farPattern = mkOption {
         type = types.str;
         default = "";
         example = "[Gmail]/Sent Mail";
         description = ''
           IMAP4 patterns for which mailboxes on the remote mail server to sync.
-          If <literal>Patterns</literal> are specified, <literal>masterPattern</literal>
+          If <literal>Patterns</literal> are specified, <literal>farPattern</literal>
           is interpreted as a prefix which is not matched against the patterns,
           and is not affected by mailbox list overrides.
           </para><para>
@@ -65,14 +65,14 @@ let
         '';
       };
 
-      slavePattern = mkOption {
+      nearPattern = mkOption {
         type = types.str;
         default = "";
         example = "Sent";
         description = ''
-          Name for where mail coming from the master mail server will end up
-          locally. The mailbox specified by the master's pattern will be placed
-          in this directory.
+          Name for where mail coming from the remote (far) mail server will end up
+          locally. The mailbox specified by the far pattern will be placed in
+          this directory.
           </para><para>
           If this is left as the default, then mbsync will default to the pattern
           <literal>INBOX</literal>.
@@ -85,7 +85,7 @@ let
         example = [ "INBOX" ];
         description = ''
           Instead of synchronizing <emphasis>just</emphasis> the mailboxes that
-          match the <literal>masterPattern</literal>, use it as a prefix which is
+          match the <literal>farPattern</literal>, use it as a prefix which is
           not matched against the patterns, and is not affected by mailbox list
           overrides.
         '';
diff --git a/modules/programs/mbsync.nix b/modules/programs/mbsync.nix
index 7d55c7343..91e7d0f77 100644
--- a/modules/programs/mbsync.nix
+++ b/modules/programs/mbsync.nix
@@ -10,6 +10,24 @@ let
   mbsyncAccounts =
     filter (a: a.mbsync.enable) (attrValues config.accounts.email.accounts);
 
+  # Given a SINGLE group's channels attribute set, return true if ANY of the channel's
+  # patterns use the invalidOption attribute set value name.
+  channelInvalidOption = channels: invalidOption:
+    any (c: c) (mapAttrsToList (c: hasAttr invalidOption) channels);
+
+  # Given a SINGLE account's groups attribute set, return true if ANY of the account's group's channel's patterns use the invalidOption attribute set value name.
+  groupInvalidOption = groups: invalidOption:
+    any (g: g) (mapAttrsToList (groupName: groupVals:
+      channelInvalidOption groupVals.channels invalidOption) groups);
+
+  # Given all accounts (ensure that accounts passed in here ARE mbsync-using accounts)
+  # return true if ANY of the account's groups' channels' patterns use the
+  # invalidOption attribute set value name.
+  accountInvalidOption = accounts: invalidOption:
+    any (a: a)
+    (map (account: groupInvalidOption account.mbsync.groups invalidOption)
+      mbsyncAccounts);
+
   genTlsConfig = tls:
     {
       SSLType = if !tls.enable then
@@ -22,10 +40,18 @@ let
       CertificateFile = toString tls.certificatesFile;
     };
 
-  masterSlaveMapping = {
+  imports = [
+    (mkRenamedOptionModule [ "programs" "mbsync" "masterSlaveMapping" ] [
+      "programs"
+      "mbsync"
+      "nearFarMapping"
+    ])
+  ];
+
+  nearFarMapping = {
     none = "None";
-    imap = "Master";
-    maildir = "Slave";
+    imap = "Far";
+    maildir = "Near";
     both = "Both";
   };
 
@@ -88,18 +114,18 @@ let
   genAccountWideChannel = account:
     with account;
     genSection "Channel ${name}" ({
-      Master = ":${name}-remote:";
-      Slave = ":${name}-local:";
+      Far = ":${name}-remote:";
+      Near = ":${name}-local:";
       Patterns = mbsync.patterns;
-      Create = masterSlaveMapping.${mbsync.create};
-      Remove = masterSlaveMapping.${mbsync.remove};
-      Expunge = masterSlaveMapping.${mbsync.expunge};
+      Create = nearFarMapping.${mbsync.create};
+      Remove = nearFarMapping.${mbsync.remove};
+      Expunge = nearFarMapping.${mbsync.expunge};
       SyncState = "*";
     } // mbsync.extraConfig.channel) + "\n";
 
   # Given the attr set of groups, return a string of channels that will direct
   # mail to the proper directories, according to the pattern used in channel's
-  # master pattern definition.
+  # "far" pattern definition.
   genGroupChannelConfig = storeName: groups:
     let
       # Given the name of the group this channel is part of and the channel
@@ -118,8 +144,8 @@ let
             else
               "";
         in genSection "Channel ${groupName}-${channel.name}" ({
-          Master = ":${storeName}-remote:${channel.masterPattern}";
-          Slave = ":${storeName}-local:${channel.slavePattern}";
+          Far = ":${storeName}-remote:${channel.farPattern}";
+          Near = ":${storeName}-local:${channel.nearPattern}";
         } // channel.extraConfig) + genChannelPatterns channel.patterns;
       # Given the group name, and a attr set of channels within that group,
       # Generate a list of strings for each channels' configuration.
@@ -206,50 +232,66 @@ in {
     };
   };
 
-  config = mkIf cfg.enable {
-    assertions = let
-      checkAccounts = pred: msg:
-        let badAccounts = filter pred mbsyncAccounts;
-        in {
-          assertion = badAccounts == [ ];
-          message = "mbsync: ${msg} for accounts: "
-            + concatMapStringsSep ", " (a: a.name) badAccounts;
-        };
-    in [
-      (checkAccounts (a: a.maildir == null) "Missing maildir configuration")
-      (checkAccounts (a: a.imap == null) "Missing IMAP configuration")
-      (checkAccounts (a: a.passwordCommand == null) "Missing passwordCommand")
-      (checkAccounts (a: a.userName == null) "Missing username")
-    ];
+  config = mkIf cfg.enable (mkMerge [
+    {
+      assertions = let
+        checkAccounts = pred: msg:
+          let badAccounts = filter pred mbsyncAccounts;
+          in {
+            assertion = badAccounts == [ ];
+            message = "mbsync: ${msg} for accounts: "
+              + concatMapStringsSep ", " (a: a.name) badAccounts;
+          };
+      in [
+        (checkAccounts (a: a.maildir == null) "Missing maildir configuration")
+        (checkAccounts (a: a.imap == null) "Missing IMAP configuration")
+        (checkAccounts (a: a.passwordCommand == null) "Missing passwordCommand")
+        (checkAccounts (a: a.userName == null) "Missing username")
+      ];
+    }
 
-    home.packages = [ cfg.package ];
+    (mkIf (accountInvalidOption mbsyncAccounts "masterPattern") {
+      warnings = [
+        "mbsync channels no longer use masterPattern. Use farPattern in its place."
+      ];
+    })
 
-    programs.notmuch.new.ignore = [ ".uidvalidity" ".mbsyncstate" ];
+    (mkIf (accountInvalidOption mbsyncAccounts "slavePattern") {
+      warnings = [
+        "mbsync channels no longer use slavePattern. Use nearPattern in its place."
+      ];
+    })
 
-    home.file.".mbsyncrc".text = let
-      accountsConfig = map genAccountConfig mbsyncAccounts;
-      # Only generate this kind of Group configuration if there are ANY accounts
-      # that do NOT have a per-account groups/channels option(s) specified.
-      groupsConfig =
-        if any (account: account.mbsync.groups == { }) mbsyncAccounts then
-          mapAttrsToList genGroupConfig cfg.groups
-        else
-          [ ];
-    in ''
-      # Generated by Home Manager.
+    {
+      home.packages = [ cfg.package ];
 
-    ''
-    + concatStringsSep "\n" (optional (cfg.extraConfig != "") cfg.extraConfig)
-    + concatStringsSep "\n\n" accountsConfig
-    + concatStringsSep "\n" groupsConfig;
+      programs.notmuch.new.ignore = [ ".uidvalidity" ".mbsyncstate" ];
 
-    home.activation = mkIf (mbsyncAccounts != [ ]) {
-      createMaildir =
-        hm.dag.entryBetween [ "linkGeneration" ] [ "writeBoundary" ] ''
-          $DRY_RUN_CMD mkdir -m700 -p $VERBOSE_ARG ${
-            concatMapStringsSep " " (a: a.maildir.absPath) mbsyncAccounts
-          }
-        '';
-    };
-  };
+      home.file.".mbsyncrc".text = let
+        accountsConfig = map genAccountConfig mbsyncAccounts;
+        # Only generate this kind of Group configuration if there are ANY accounts
+        # that do NOT have a per-account groups/channels option(s) specified.
+        groupsConfig =
+          if any (account: account.mbsync.groups == { }) mbsyncAccounts then
+            mapAttrsToList genGroupConfig cfg.groups
+          else
+            [ ];
+      in ''
+        # Generated by Home Manager.
+
+      ''
+      + concatStringsSep "\n" (optional (cfg.extraConfig != "") cfg.extraConfig)
+      + concatStringsSep "\n\n" accountsConfig
+      + concatStringsSep "\n" groupsConfig;
+
+      home.activation = mkIf (mbsyncAccounts != [ ]) {
+        createMaildir =
+          hm.dag.entryBetween [ "linkGeneration" ] [ "writeBoundary" ] ''
+            $DRY_RUN_CMD mkdir -m700 -p $VERBOSE_ARG ${
+              concatMapStringsSep " " (a: a.maildir.absPath) mbsyncAccounts
+            }
+          '';
+      };
+    }
+  ]);
 }
diff --git a/tests/modules/programs/mbsync/mbsync-expected.conf b/tests/modules/programs/mbsync/mbsync-expected.conf
index 672296047..c1ca921ac 100644
--- a/tests/modules/programs/mbsync/mbsync-expected.conf
+++ b/tests/modules/programs/mbsync/mbsync-expected.conf
@@ -16,30 +16,30 @@ Path /home/hm-user/Mail/hm-account/
 SubFolders Verbatim
 
 Channel emptyChannels-empty1
-Master :hm-account-remote:
-Slave :hm-account-local:
+Far :hm-account-remote:
+Near :hm-account-local:
 
 Channel emptyChannels-empty2
-Master :hm-account-remote:
-Slave :hm-account-local:
+Far :hm-account-remote:
+Near :hm-account-local:
 
 Channel hm-account-earlierPatternMatch
-Master :hm-account-remote:Label
-Slave :hm-account-local:SomethingUnderLabel
+Far :hm-account-remote:Label
+Near :hm-account-local:SomethingUnderLabel
 Pattern ThingUnderLabel !NotThisMaildirThough "[Weird] Label?"
 
 Channel hm-account-inbox
-Master :hm-account-remote:Inbox
-Slave :hm-account-local:Inbox
+Far :hm-account-remote:Inbox
+Near :hm-account-local:Inbox
 
 Channel hm-account-patternMatch
-Master :hm-account-remote:Label
-Slave :hm-account-local:SomethingUnderLabel
+Far :hm-account-remote:Label
+Near :hm-account-local:SomethingUnderLabel
 Pattern ThingUnderLabel !NotThisMaildirThough "[Weird] Label?"
 
 Channel hm-account-strangeHostBoxName
-Master ":hm-account-remote:[Weird]/Label Mess"
-Slave :hm-account-local:[AnotherWeird]/Label
+Far ":hm-account-remote:[Weird]/Label Mess"
+Near :hm-account-local:[AnotherWeird]/Label
 
 Group emptyChannels
 Channel emptyChannels-empty1
@@ -68,12 +68,12 @@ Path /home/hm-user/Mail/hm@example.com/
 SubFolders Verbatim
 
 Channel inboxes-inbox1
-Master :hm@example.com-remote:Inbox1
-Slave :hm@example.com-local:Inboxes
+Far :hm@example.com-remote:Inbox1
+Near :hm@example.com-local:Inboxes
 
 Channel inboxes-inbox2
-Master :hm@example.com-remote:Inbox2
-Slave :hm@example.com-local:Inboxes
+Far :hm@example.com-remote:Inbox2
+Near :hm@example.com-local:Inboxes
 
 Group inboxes
 Channel inboxes-inbox1
diff --git a/tests/modules/programs/mbsync/mbsync-master-slave-change.nix b/tests/modules/programs/mbsync/mbsync-master-slave-change.nix
new file mode 100644
index 000000000..96f02d906
--- /dev/null
+++ b/tests/modules/programs/mbsync/mbsync-master-slave-change.nix
@@ -0,0 +1,93 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+{
+  imports = [ ../../accounts/email-test-accounts.nix ];
+
+  test.asserts.warnings.expected = [
+    "mbsync channels no longer use masterPattern. Use farPattern in its place."
+    "mbsync channels no longer use slavePattern. Use nearPattern in its place."
+  ];
+
+  config = {
+    programs.mbsync = {
+      enable = true;
+      # programs.mbsync.groups and
+      # accounts.email.accounts.<name>.mbsync.groups should NOT be used at the
+      # same time.
+      # If they are, then the new version will take precendence.
+      groups.inboxes = {
+        "hm@example.com" = [ "Inbox1" "Inbox2" ];
+        hm-account = [ "Inbox" ];
+      };
+    };
+
+    accounts.email.accounts = {
+      "hm@example.com".mbsync = {
+        enable = true;
+        groups.inboxes = {
+          channels = {
+            inbox1 = {
+              farPattern = "Inbox1";
+              nearPattern = "Inboxes";
+            };
+            inbox2 = {
+              farPattern = "Inbox2";
+              nearPattern = "Inboxes";
+            };
+          };
+        };
+      };
+
+      hm-account.mbsync = {
+        enable = true;
+        groups.hm-account = {
+          channels.earlierPatternMatch = {
+            farPattern = "Label";
+            nearPattern = "SomethingUnderLabel";
+            patterns = [
+              "ThingUnderLabel"
+              "!NotThisMaildirThough"
+              ''"[Weird] Label?"''
+            ];
+          };
+          channels.inbox = {
+            farPattern = "Inbox";
+            nearPattern = "Inbox";
+          };
+          channels.strangeHostBoxName = {
+            farPattern = "[Weird]/Label Mess";
+            nearPattern = "[AnotherWeird]/Label";
+          };
+          channels.patternMatch = {
+            farPattern = "Label";
+            nearPattern = "SomethingUnderLabel";
+            patterns = [
+              "ThingUnderLabel"
+              "!NotThisMaildirThough"
+              ''"[Weird] Label?"''
+            ];
+          };
+        };
+        # No group should be printed.
+        groups.emptyGroup = { };
+        # Group should be printed, but left with default channels.
+        groups.emptyChannels = {
+          channels.empty1 = { };
+          channels.empty2 = { };
+        };
+      };
+    };
+
+    test.asserts.warnings.expected = [
+      "mbsync channels no longer use masterPattern. use farPattern in its place."
+      "mbsync channels no longer use slavePattern. Use nearPattern in its place."
+    ];
+
+    nmt.script = ''
+      assertFileExists home-files/.mbsyncrc
+      assertFileContent home-files/.mbsyncrc ${./mbsync-expected.conf}
+    '';
+  };
+}
diff --git a/tests/modules/programs/mbsync/mbsync.nix b/tests/modules/programs/mbsync/mbsync.nix
index a6e555cd4..d80421d6d 100644
--- a/tests/modules/programs/mbsync/mbsync.nix
+++ b/tests/modules/programs/mbsync/mbsync.nix
@@ -24,12 +24,12 @@ with lib;
         groups.inboxes = {
           channels = {
             inbox1 = {
-              masterPattern = "Inbox1";
-              slavePattern = "Inboxes";
+              farPattern = "Inbox1";
+              nearPattern = "Inboxes";
             };
             inbox2 = {
-              masterPattern = "Inbox2";
-              slavePattern = "Inboxes";
+              farPattern = "Inbox2";
+              nearPattern = "Inboxes";
             };
           };
         };
@@ -39,8 +39,8 @@ with lib;
         enable = true;
         groups.hm-account = {
           channels.earlierPatternMatch = {
-            masterPattern = "Label";
-            slavePattern = "SomethingUnderLabel";
+            farPattern = "Label";
+            nearPattern = "SomethingUnderLabel";
             patterns = [
               "ThingUnderLabel"
               "!NotThisMaildirThough"
@@ -48,16 +48,16 @@ with lib;
             ];
           };
           channels.inbox = {
-            masterPattern = "Inbox";
-            slavePattern = "Inbox";
+            farPattern = "Inbox";
+            nearPattern = "Inbox";
           };
           channels.strangeHostBoxName = {
-            masterPattern = "[Weird]/Label Mess";
-            slavePattern = "[AnotherWeird]/Label";
+            farPattern = "[Weird]/Label Mess";
+            nearPattern = "[AnotherWeird]/Label";
           };
           channels.patternMatch = {
-            masterPattern = "Label";
-            slavePattern = "SomethingUnderLabel";
+            farPattern = "Label";
+            nearPattern = "SomethingUnderLabel";
             patterns = [
               "ThingUnderLabel"
               "!NotThisMaildirThough"