I turned on logging.
Below are the contents.
Everything looks pretty normal.
[20-Feb-2017 16:34:38 -0600]: <viu6c26n> Recv: 220 mydomain.com ESMTP Sendmail 8.15.2/8.15.2; Mon, 20 Feb 2017 16:34:38 -0600
[20-Feb-2017 16:34:38 -0600]: <viu6c26n> Send: EHLO mydomain.com
[20-Feb-2017 16:34:38 -0600]: <viu6c26n> Recv: 250-mydomain.com Hello localhost [127.0.0.1], pleased to meet you
[20-Feb-2017 16:34:38 -0600]: <viu6c26n> Recv: 250-ENHANCEDSTATUSCODES
[20-Feb-2017 16:34:38 -0600]: <viu6c26n> Recv: 250-PIPELINING
[20-Feb-2017 16:34:38 -0600]: <viu6c26n> Recv: 250-8BITMIME
[20-Feb-2017 16:34:38 -0600]: <viu6c26n> Recv: 250-SIZE
[20-Feb-2017 16:34:38 -0600]: <viu6c26n> Recv: 250-AUTH GSSAPI
[20-Feb-2017 16:34:38 -0600]: <viu6c26n> Recv: 250-STARTTLS
[20-Feb-2017 16:34:38 -0600]: <viu6c26n> Recv: 250-DELIVERBY
[20-Feb-2017 16:34:38 -0600]: <viu6c26n> Recv: 250 HELP
[20-Feb-2017 16:34:38 -0600]: <viu6c26n> Send: MAIL FROM:<myaddress@mydomain.com>
[20-Feb-2017 16:34:38 -0600]: <viu6c26n> Recv: 250 2.1.0 <myaddress@mydomain.com>... Sender ok
[20-Feb-2017 16:34:38 -0600]: <viu6c26n> Send: RCPT TO:<blah@blahblah.blah>
[20-Feb-2017 16:34:38 -0600]: <viu6c26n> Recv: 250 2.1.5 <blah@blahblah.blah>... Recipient ok
[20-Feb-2017 16:34:38 -0600]: <viu6c26n> Send: DATA
[20-Feb-2017 16:34:38 -0600]: <viu6c26n> Recv: 354 Enter mail, end with "." on a line by itself
[20-Feb-2017 16:34:38 -0600]: <viu6c26n> Send: MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII;
format=flowed
Content-Transfer-Encoding: 7bit
Date: Mon, 20 Feb 2017 16:34:38 -0600
From: myaddress <myaddress@mydomain.com>
To: Blah <blah@blahblah.blah>
Subject: test
Message-ID: <52ce981621113b0c4cfd765f3b78eef0@mydomain.com>
X-Sender: myaddress@mydomain.com
User-Agent: Roundcube Webmail/1.1.4
test
[20-Feb-2017 16:34:38 -0600]: <viu6c26n> Send: .
[20-Feb-2017 16:34:38 -0600]: <viu6c26n> Recv: 250 2.0.0 v1KMYcT2000981 Message accepted for delivery
[20-Feb-2017 16:34:39 -0600]: <viu6c26n> Send: QUIT
[20-Feb-2017 16:34:39 -0600]: <viu6c26n> Recv: 221 2.0.0 mydomain.com closing connection