Very interesting, can you elaborate on this on where exactly you are getting the errors and bounce backs?
I've spent the afternoon looking over the setting as this would be concerning if this was default behavior.
What I am seeing
- The default postfix (actual software that sends/receives the mail) is set at 100MB, and I can easily receive emails upto this.
- Sending works fine in Outlook upto 20MB by IMAP/SMTP
- Attaching large files past 20MB in webmail (via the controller) gives a Error 500 and does not attach. I put this down to usual latency/bs issues similar to phpMyAdmin.
- Attaching large files past 20MB in webmail (via the mail servers) works fine
- Max upload in roundcube is 75MB and logical for a 100MB postfix max size. This is likely controlled by the php upload size but I'll let the team recommend the way to set this which wont get overridden.
- There does not appear to be any funky restrictions or limits set in postfix or dovecot.
On your email server can you check your postfix email size and share more details on the bounce errors you are getting?
This can be done by looking for the 'message_size_limit' expressed in bytes under
/etc/postfix/master.cf
By default it should be 100MB and I haven't received any complaints yet.
Alternatively you can type the following to get this value. It should be '102400000' bytes
postconf message_size_limit
An a off chance, are you using any mail-filtering solutions infront of enhance?
As to sending large emails, 20MB is the industry standard limit what you should aim for. Beyond this you are at the mercy of the receiving email server and the various spam/anti virus filters accepting it.
Do note a 20MB attachment when sent could be 1.5 larger due to how its encoded, so a maximum real size of an email could easily be under 20MB.
Outlook has a 20MB restriction baked into the email client which can be changed if you're feeling lucky:
https://learn.microsoft.com/en-US/outlook/troubleshoot/message-body/attachment-size-exceeds-the-allowable-limit-error
Yes Office365 & Google Workspaces can do larger, but these platforms work in weirder more mysterious untraditional ways.
Emails should never be over 100MB! Tell them to use dropbox and send a URL.
Email is not designed for sending large files. Stand your ground and demand trial by combat if some dumb-ass user/employee refuses to accept they can't email their 1.4GB video.
+1 on that these values should be configured in the settings and consistent or at-least documented
