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The SMTP communication looks a little odd. Using "Follow -> TCP Stream" gives the following SMTP communication:

220-server.thesmithcloud.com ESMTP Postfix
EHLO localhost
220 server.thesmithcloud.com ESMTP Postfix
HELO localhost
250-server.thesmithcloud.com
250-PIPELINING
250-SIZE
250-VRFY
250-ETRN
250-STARTTLS
250-AUTH LOGIN PLAIN CRAM-MD5 DIGEST-MD5 GSSAPI
250-ENHANCEDSTATUSCODES
250-8BITMIME
250-DSN
250-SMTPUTF8
250-BINARYMIME
250 CHUNKING
AUTH LOGIN
250 server.thesmithcloud.com
QUIT
334 VXNlcm5hbWU6
334 UGFzc3dvcmQ6

It's odd because the client, after sending the EHLO then sends a superfluous HELO.

The server continues it's response to the EHLO with the set of 250- responses, ending with the 250 CHUNKING (no dash after the 250 signals the end of the set).

The client then sends the AUTH LOGIN request and instead of the expected 334 VXNlcm5hbWU6 (Base64 encoding of "Username") receives the 250 response from the HELO request and the client then terminates the conversation with QUIT.

The server then does send the responses to the AUTH LOGIN but the client has given up and responds with a TCP RST.

I have no idea why the client is behaving this way.

FYI, a reasonable primer on the SMTP protocol can be found here.