There are several issues here.  First, you do not belong on this list if
you cannot handle large e-mails, nor frequent ones.

That said, I have a 400k limit on posts.  (It was 200k, but that was too
small.)  The traditional limit is 100k, and historical sites sometimes
enforce this limit.  Most sites have no limit, and can handle 10meg
attachments with ease.  A few have a ~4meg limit.  (There's a bug in BSD
that causes that very specific number.  Computer geeks will recognize
why.)

In summary, chop it into 350k size bites.