Thanks, for me it looks like the camera terminates/quit the TLS session before the authentication. Everything looks ok in the mail server log. Unfortunately the logging in the camera is very sparse so it's not possible to tell why the camera quit the session.
Below you will see the fail interaction
2019-08-30 08:08:08 xxxxxxxxx sendmail[18794]: STARTTLS=server, relay=[192.168.42.204], version=TLSv1, verify=NOT, cipher=ECDHE-RSA-AES256-SHA, bits=256/256
2019-08-30 08:08:08 xxxxxxxxx sendmail[18794]: STARTTLS=server, cert-subject=, cert-issuer=, verifymsg=ok
2019-08-30 08:08:08 xxxxxxxxx sendmail[18794]: AUTH: available mech=GSS-SPNEGO GSSAPI LOGIN PLAIN, allowed mech=EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN
2019-08-30 08:08:08 xxxxxxxxx sendmail[18794]: STARTTLS=read, info: fds=7/4, err=2
2019-08-30 08:08:08 xxxxxxxxx sendmail[18794]: x7U681bh018794: <-- QUIT
2019-08-30 08:08:08 xxxxxxxxx sendmail[18794]: x7U681bh018794: --- 221 2.0.0 xxxxxxxxx.com closing connection
This is how it looks from a camera that works
2019-08-29 19:36:01 xxxxxxxxxx sendmail[3431]: x7THZuRj003431: --- 220 2.0.0 Ready to start TLS
2019-08-29 19:36:04 xxxxxxxxxx sendmail[3431]: STARTTLS=server, get_verify: 0 get_peer: 0x0
2019-08-29 19:36:04 xxxxxxxxxx sendmail[3431]: STARTTLS=server, relay=nn-nnn-nnn-nn.foobar.frotz.net [nn.nnn.nnn.nn], version=TLSv1, verify=NOT, cipher=DHE-RSA-AES256-SHA, bits=256/256
2019-08-29 19:36:04 xxxxxxxxxx sendmail[3431]: STARTTLS=server, cert-subject=, cert-issuer=, verifymsg=ok
2019-08-29 19:36:04 xxxxxxxxxx sendmail[3431]: AUTH: available mech=GSS-SPNEGO GSSAPI LOGIN PLAIN, allowed mech=EXTERNAL GSSAPI DIGEST-MD5 CRAM-MD5 LOGIN PLAIN
2019-08-29 19:36:04 xxxxxxxxxx sendmail[3431]: STARTTLS=read, info: fds=7/4, err=2
2019-08-29 19:36:04 xxxxxxxxxx sendmail[3431]: x7THZuRj003431: <-- EHLO smtp.txt
2019-08-29 19:36:04 xxxxxxxxxx sendmail[3431]: x7THZuRk003431: milter=greylist, action=helo, continue
2019-08-29 19:36:04 xxxxxxxxxx sendmail[3431]: x7THZuRj003431: <-- EHLO smtp.txt