Postfix default message limit
By default postfix has a message limit size of 10 megabytes. In today's world you may want to change this amount to be much higher, and you may want to allow larger mailbox sizes in general as well. You can do this with a few commands on your server:
that command will show you what the defaults are, you can do a
postconf -d | grep limit
to see what all your limits are defaulted to
will show you what you've explicitly set
postconf -e "message_size_limit = 102400000"
postconf -e "mailbox_size_limit = 512000000"
postconf -e "virtual_mailbox_limit = 512000000"
This will set your message size limit to roughly 100mb and your mailbox sizes to roughly 500mb
You can change these amounts for your server, the options are set in bytes. If you don't want to do any math at all, you can always use google to do the conversion. Just search something like "200 megabytes in bytes" in google and it's calculator will tell you what 200mb is in bytes. The google calculator return value has some spaces in the number, so just make sure to remove those before using them in your configuration.