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 * 1165) = 50
c ~> ('a' * 899 + '\r\n') * 1165
# We have 50 characters left before the message is too big.
c ~> 'b' * 55 + '\r\n'
# At this point the message is too big. The remainder data should be
# discarded.
# We use a "bad ." to try to do an SMTP smuggling attack.
c ~> '.\n'
c -> HELP
c -> HELP
# And now the "good .".
c -> .
c <- 521 5.5.2 Error reading DATA: invalid line ending