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After upgrade to 38.3 cannot send outgoing messages

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I made a mistake and accidentally upgraded to Thunderbird 38.3 on my MacBook running El Captain. Now when I try to send emails from Thunderbird, I get a cannot connect to the outgoing server for an unknown reason message. All outgoing server settings are correct as certified by our university IT people. Exactly the same thing happened on my PC previously and no help from anyone was ever able to correct it. I can open, connect and download messages fine. I only have trouble sending messages and connecting to the outgoing server. This started with TB ver. 38.2 on my PC and now 38.3 on my Mac. Very irritating. Have had to switch to Outlook as my email client on my PC and now will have to find a new client for my Mac. Prior versions of Thunderbird have always worked fine. I have no idea what then new upgraded have that are making them do this with our enterprise exchange system, but we are all having to abandon Thunderbird now. Has anyone else had this problem? Any thoughts on how to correct it? I posted this problem before, but none of the suggestions were about this problem or helped.

I made a mistake and accidentally upgraded to Thunderbird 38.3 on my MacBook running El Captain. Now when I try to send emails from Thunderbird, I get a cannot connect to the outgoing server for an unknown reason message. All outgoing server settings are correct as certified by our university IT people. Exactly the same thing happened on my PC previously and no help from anyone was ever able to correct it. I can open, connect and download messages fine. I only have trouble sending messages and connecting to the outgoing server. This started with TB ver. 38.2 on my PC and now 38.3 on my Mac. Very irritating. Have had to switch to Outlook as my email client on my PC and now will have to find a new client for my Mac. Prior versions of Thunderbird have always worked fine. I have no idea what then new upgraded have that are making them do this with our enterprise exchange system, but we are all having to abandon Thunderbird now. Has anyone else had this problem? Any thoughts on how to correct it? I posted this problem before, but none of the suggestions were about this problem or helped.

All Replies (6)

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Do you see anything relevant in the error console? Tools (Alt-T) - Error Console

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attached is a screen shot of the error message I get and a screen shot of my current outgoing server settings. I have doubled checked with my university and these settings are correct. These are the same settings that I had used for years prior to this update version. This same problem has happened with my MacBook running El Capitan and a Dell laptop running Windows 7.1 Pro. Obviously there is some sort of conflict between the university Exchange server system and the new version of Thunderbird. Any thoughts on how to resolve this appreciated. I have contacted the IT office at the university and put in a request for help.

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I was looking for any messages from the Error Console. https://support.mozilla.org/en-US/questions/1093959#answer-805992

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Sorry, did not know about the Error Console. Attached is a screen shot. The first 3 messages were there when I opened Thunderbird. The last two appeared after trying to send a message and getting the error message in the screen shot in the previous message. I have seen reference to Diffie-Hellman in some of the other posts. Any thoughts on how to correct this?

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Chosen Solution

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Thanks. After some work trying to figure out how to download the actual add-on file (Firefox seems to just have Add to Firefox, so used IE) and locating the menu item in Firefox for using an add-on file, successfully installed the Disable DHE add-on. Sending files now work. Will alert our university email system folks to this vulnerability. Thanks for your help.