[Geary] Unable to validate Exchange SMTP server

[Grant Edwards <grant b edwards gmail com>]

I'm trying to set up Geary 0.12.4 with Exchange server IMAP+SMTP.

IMAP seems to connect fine.  Various other SMTP clients work fine
(mutt, msmtp, Android Gmail app, IOS email app, Python smtplib), but
Geary can't seem to authenticate.  Using Wireshark, I can see the
connection get established, the starttls command, and the TLS
hadshaking, some "application data" is exchanged", then there's a TLS
alert when the connection is closed.

Is there any way to log the plaintext SMTP traffic?

Here's what I get when I run geary --debug and try to create the account:

 [deb] 17:01:30 115.416164 geary-controller.vala:898: User entered revised account information, retrying 
validation
 [deb] 17:01:30 0.066451 imap-client-session.vala:1469: [0002/exchange.[...].com/default:993 
GEARY_IMAP_CLIENT_SESSION_STATE_CONNECTING] Connected to exchange.[...].com/default:993
 [deb] 17:01:30 0.000006 imap-client-session.vala:624: [0002/exchange.[...].com/default:993 
GEARY_IMAP_CLIENT_SESSION_STATE_CONNECTING] Connected
 [deb] 17:01:30 0.053611 imap-client-session.vala:1542: [0002/exchange.[...].com/default:993 
GEARY_IMAP_CLIENT_SESSION_STATE_NOAUTH] capability #1: NAMESPACE IMAP4rev1 IMAP4 "AUTH=GSSAPI" "AUTH=PLAIN" 
"AUTH=NTLM" UIDPLUS MOVE CHILDREN ID LITERAL+ IDLE
 [deb] 17:01:30 0.000373 imap-client-session.vala:718: [0002/exchange.[...].com/default:993 
GEARY_IMAP_CLIENT_SESSION_STATE_NOAUTH] use_starttls=false is_ssl=true starttls=false
 [deb] 17:01:30 0.000007 imap-client-session.vala:746: [0002/exchange.[...].com/default:993 
GEARY_IMAP_CLIENT_SESSION_STATE_NOAUTH] No STARTTLS attempted
 [deb] 17:01:30 0.694583 imap-client-session.vala:1542: [0002/exchange.[...].com/default:993 
GEARY_IMAP_CLIENT_SESSION_STATE_AUTHORIZED] capability #2: NAMESPACE IMAP4rev1 IMAP4 "AUTH=GSSAPI" 
"AUTH=PLAIN" "AUTH=NTLM" UIDPLUS XPROXY3 MOVE CHILDREN ID LITERAL+ IDLE
 [deb] 17:01:30 0.000158 imap-client-session.vala:782: [0002/exchange.[...].com/default:993 
GEARY_IMAP_CLIENT_SESSION_STATE_AUTHORIZED] No compression available
 [deb] 17:01:30 0.000022 imap-deserializer.vala:251: [des:0002/GEARY_IMAP_DESERIALIZER_STATE_TAG] Waiting for 
deserializer to close...
 [deb] 17:01:30 0.000078 imap-deserializer.vala:822: [des:0002/GEARY_IMAP_DESERIALIZER_STATE_TAG] input 
error: Operation was cancelled
 [deb] 17:01:30 0.000037 imap-deserializer.vala:253: [des:0002/GEARY_IMAP_DESERIALIZER_STATE_CLOSED] 
Deserializer closed
 [deb] 17:01:30 0.000010 imap-client-connection.vala:422: 
[0002/exchange.[...].com/default:993/GEARY_IMAP_CLIENT_CONNECTION_STATE_CONNECTED] Disconnecting...
 [deb] 17:01:30 0.000093 imap-client-connection.vala:425: 
[0002/exchange.[...].com/default:993/GEARY_IMAP_CLIENT_CONNECTION_STATE_CONNECTED] Disconnected
 [deb] 17:01:30 0.000005 imap-client-session.vala:1475: [0002/exchange.[...].com/default:993 
GEARY_IMAP_CLIENT_SESSION_STATE_BROKEN] Disconnected from exchange.[...].com/default:993
 [deb] 17:01:30 0.000055 imap-client-session.vala:406: DTOR: ClientSession exchange.[...].com/default:993 
GEARY_IMAP_CLIENT_SESSION_STATE_BROKEN
 [deb] 17:01:31 0.187584 smtp-client-session.vala:102: [exchange.[...].com/default:25] Attempting PLAIN 
authenticator
 [deb] 17:01:36 5.061306 smtp-client-session.vala:102: [exchange.[...].com/default:25] Attempting LOGIN 
authenticator
 [deb] 17:01:41 5.078203 geary-engine.vala:370: Error validating SMTP account info: Unable to authenticate 
with exchange.[...].com/default:25
 [deb] 17:01:41 0.101284 geary-controller.vala:886: Validation failed. Prompting user for revised account 
information
 [deb] 17:05:48 246.995971 geary-controller.vala:978: User refused to enter account information. Exiting...
 [deb] 17:05:48 0.010506 geary-controller.vala:379: Flushing avatar cache...
 [deb] 17:05:48 0.000022 geary-controller.vala:385: Closing Engine...
 [deb] 17:05:48 0.000103 geary-controller.vala:387: Closed Engine