This is bigger than GMail allows sending (25MB,
https://support.google.com/mail/answer/6584?hl=en&co=GENIE.Platform%3DDesktop#zippy=%2Cattachment-size-limit),
but smaller than they allow receiving (50MB,
https://support.google.com/a/answer/
1366776?hl=en).
# See https://wiki.dovecot.org/LDA/Postfix
mailbox_size_limit = 512000000
+# Max message size 40MB
+message_size_limit = 41943040
+
# The mailbox_transport specifies the optional transport in master.cf
# to use after processing aliases and .forward files. This parameter
# has precedence over the mailbox_command, fallback_transport and