With the latest Thunderbird beta (TB38.0b6) I cannot get mail from Exchange anymore using STARTTLS. I have configured connection security STARTTLS, authentication method Normal password. This works with TB31.7.0. When I change the connection security to None, I can again receive mail. In the error console there are no messages. In the IMAP logging, I see a message "login failed completely". I have tried different connection securities and/or authentication methods, but only None/Normal password seems to work.

Same error here. Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 Fedora 22. Library Versions Expected minimum version Version in use NSPR 4.10.8 4.10.8 NSS 3.18 Basic ECC 3.19.1 Extended ECC NSS Util 3.18 3.19.1 NSS SSL 3.18 Basic ECC 3.19.1 Extended ECC NSS S/MIME 3.18 Basic ECC 3.19.1 Extended ECC

Same problem here (package thunderbird 1:38.2.0+build1-0ubuntu0). It was working OK until 2/8/2015. Here's the debug log while opening a folder in the exchange server after leaving offline mode: 2015-09-21 18:00:47.138749 UTC - -764467456[7f75c2ac5c00]: ImapThreadMainLoop entering [this=d3066000] 2015-09-21 18:00:47.138992 UTC - 234219392[7f760cb38580]: d3066000:server.domain:NA:SetupWithUrl: clearing IMAP_CONNECTION_IS_OPEN 2015-09-21 18:00:47.139806 UTC - -764467456[7f75c2ac5c00]: d3066000:server.domain:NA:ProcessCurrentURL: entering 2015-09-21 18:00:47.139967 UTC - -764467456[7f75c2ac5c00]: d3066000:server.domain:NA:ProcessCurrentURL:imap://username%40domain%2Ees@server.domain:993/select%3E/Borradores: = currentUrl 2015-09-21 18:00:47.327500 UTC - -764467456[7f75c2ac5c00]: ReadNextLine [stream=cf396600 nb=101 needmore=0] 2015-09-21 18:00:47.327591 UTC - -764467456[7f75c2ac5c00]: d3066000:server.domain:NA:CreateNewLineFromSocket: * OK Servidor IMAP4rev1de Microsoft Exchange Server ready. 2015-09-21 18:00:47.337050 UTC - -764467456[7f75c2ac5c00]: d3066000:server.domain:NA:SendData: 1 capability 2015-09-21 18:02:27.465166 UTC - -764467456[7f75c2ac5c00]: ReadNextLine [stream=cf396600 nb=0 needmore=1] 2015-09-21 18:02:27.465521 UTC - -764467456[7f75c2ac5c00]: d3066000:server.domain:NA:CreateNewLineFromSocket: clearing IMAP_CONNECTION_IS_OPEN - rv = 804b000e 2015-09-21 18:02:27.469112 UTC - -764467456[7f75c2ac5c00]: d3066000:server.domain:NA:TellThreadToDie: close socket connection 2015-09-21 18:02:27.469299 UTC - -764467456[7f75c2ac5c00]: d3066000:server.domain:NA:CreateNewLineFromSocket: (null) 2015-09-21 18:02:27.473534 UTC - -764467456[7f75c2ac5c00]: d3066000:server.domain:NA:ProcessCurrentURL: aborting queued urls 2015-09-21 18:02:27.474513 UTC - -764467456[7f75c2ac5c00]: ImapThreadMainLoop leaving [this=d3066000]

I can confirm this issue too. I am trying to connect to an exchange server configured with STARTTLS, and Thunderbird hangs indefinitely with ""Checking mail server capabilities..."

Onno, do you still see this issue?

No, this seems to work in TB48.4.0. I haven't tried interim versions to see if it was already fixed earlier, e.g. in TB38.0 Release version, so I don't know the regression range or what caused this and what fixed it, but for me the problem doesn;t occur anymore.