diff --git a/modules/programs/msmtp.nix b/modules/programs/msmtp.nix
index 7c1ee0d3c..f8ba6a6f7 100644
--- a/modules/programs/msmtp.nix
+++ b/modules/programs/msmtp.nix
@@ -53,6 +53,11 @@ in {
         description = ''
           Extra configuration lines to add to <filename>~/.msmtprc</filename>.
           See <link xlink:href="https://marlam.de/msmtp/msmtprc.txt"/> for examples.
+          </para><para>
+          Note, if running msmtp fails with the error message "account default
+          was already defined" then you probably have an account command here.
+          Account commands should be placed in
+          <xref linkend="opt-accounts.email.accounts._name_.msmtp.extraConfig"/>.
         '';
       };