c tcp_connect localhost:1025

c <~ 220
c -> EHLO localhost
c <... 250 HELP
c -> MAIL FROM: <>
c <~ 250
c -> RCPT TO: user@testserver
c <~ 250
c -> DATA
c <~ 354
c -> Subject: Message too big
c -> 

# Max message size is 1 MiB. Note this includes line endings but converted to
# \n (as per textproto.DotReader), and excluding the final ".".
# We already sent (in the header) 26.
# Send lines of len 900 to stay under the limit.
# (1024 * 1024 - 26) - (900 * 1166) = -850
c ~> ('a' * 899 + '\r\n') * 1166

c -> .

c <~ 552 5.3.4 Message too big
c -> QUIT
c <~ 221