The other machine says it is ready by
sending the number 220 and its fully qualified hostname (the only required information).
If the other machine is running sendmail, it may also say the program name is
sendmail and state the version. It may also state that it is ready and gives its idea of
the local date and time.
The ESMTP means that the remote site understands Extended SMTP.
If sendmail waits too long for a connection without receiving this initial message, it
prints ???Connection timed out??? and queues the mail message for later delivery.
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26 | Chapter 1: Some Basics
Next, the local sendmail sends (the >>>) the word EHLO, for Extended Hello, and its
own hostname:
>>> EHLO here.us.edu
250-remote.domain Hello here.us.edu [123.45.67.89], pleased to meet you
250-ENHANCEDSTATUSCODES
250-8BITMIME
250-SIZE
250-DSN
250-ETRN
250-DELIVERBY
250 HELP
The E of the EHLO says that the local sendmail speaks ESMTP too. The remote
machine replies with 250, then lists the ESMTP services that it supports. All but the
last reply line contain a dashfollowing the 250. That dash signals that an additional
reply line will follow. The last line, the HELP line, lacks a dash, and so completes the
reply.
One problem that could occur is your machine sending a short hostname (???here???) in
the EHLO message.
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