Allow to configure maximum email size

[adbenitez]

Is your feature request related to a problem? Please describe.
I can't send attachments bigger than 1MB, currently the server can only be used for text message and small files.

Describe the solution you'd like
Make maximum email size configurable via CLI option, ex. -maxsize or so. Also 1MB is too small in modern times, usually email servers allow 25-50MB, not to say this is a server you probably self-host for yourself, so would be good to set 50MB as default limit, or even "no limit" by default.

Describe alternatives you've considered
Changing the hard-coded value and compiling a custom yggmail :)

Additional context
I am using yggmail with Delta Chat, where it is easy to send animated stickers, gifs and other files, as well as recording voice messages and videos, 1MB is too low

[cyBerta]

@neilalexander I would be interested in helping with this feature, especially for the multicast-only use-case. Is there a particular reason why app only supports 1MB messages? Just increasing the hard-coded limit, or setting it to 0 (unlimited) seems not solve completely this issue. Sending larger messages just results in failing TCP connections, however I couldn't yet figure out exactly why. If you have any pointers or background info, it would be awesome if you could share them.

[d47081]

Agreed, most useful feature is scalable attachment size on self-hosted server, and 1Mb is too small for most needs