Mail delivery notices are correctly delivered, actual mail isn't

example in log:

[email protected] R=smarthost T=remote_smtp_smarthost: message is too big (transport limit = 1)

this means a max LINE limit of 998 chars has been hit

solution:

in "/etc/exim4/exim4.conf.localmacros" add the following line:

IGNORE_SMTP_LINE_LENGTH_LIMIT = 1

and then restart exim4.

I think you've hit this reported bug, exim4: bogus reject response on overlong lines.

It actually refers to lines that are too long, not the message itself. Try piping your message through fmt -s before passing it to exim4.