Is “MTA Settings” the only place where message size is set? I have a client inquiring about attachment size and I want to make sure I’m not missing a limit somewhere. I currently have it set to 50 megs.
I’m not sure about regular desktop clients connecting remotely, but I’ve been working on attachment limits for the webmail apps. Maybe some of this info helps?
/home/interworx/etc/php.ini
file_uploads = On
max_execution_time = 900
max_input_time = 600
memory_limit = 64M
upload_max_filesize = 20M
post_max_size = 20M
The post_max_size value in php.ini is where the webmail apps get the “max” number displayed when composing.
For Mysql you may already have a packet limit of 128M which seems too large and I cut that number in half same way I did in php.ini for memory_limit. So far so good.
/home/interworx/etc/my.cnf
max_allowed_packet = 64M
Qmail also has a limit that should be roughly the same as post_max_size. Look in
/var/qmail/control/databytes
The Squirrel has good docs if webmail is your issue:
http://www.squirrelmail.org/wiki/AttachmentSize
I believe NodeWorx MTA settings set this number /var/qmail/control/databytes
Good point, which answer’s johan_hammy’s question more succinctly than I did. 
Webmail on the brain syndrome.