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Thunderbird not signing in on one computer

  • 6 replies
  • 1 has this problem
  • Last reply by cbrown4

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After working for years, I am unable to sign into one account out of three set up in Thunderbird on a windows computer. Another windows computer and a linux (ubuntu) computer work fine with exactly the same settings, as they have for years.

Why would I suddenly be unable to sign in on one account in one computer, when it has the same settings as other computers that work. Would something have changed on the one (W10) computer that could prevent signing in on one account?

Chosen solution

Thank you for your help and concern. With this information, it seems that the easiest solution will be to move to another email client.

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All Replies (6)

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if two different computer has two different version of TB (Thunderbird), lets say one is using v68 series , another is v78 series, then this can happen. (as v68 & v78 series TB has some big differences)

if one has such AV/FW/SS software , that is different than another computer , then this can happen.

after an update/upgrade , AV/FW/SS software begins to intercept mail-server network traffic again , so that can be problematic too.


so, disable "mail-protection" option in your AV/FW/SS software unless that option has a sub-option of adding EXCEPTIONS , if it has, then add IMAP/POP3, SMTP,etc as exception . if sub-option does not exist then disable "mail protection" option only . keep the "Scan files on access" option enabled in your AV/FW/SS software . also see this earlier answer (PART-3 & PART-4) on AV/FW/SS , what else you have to configure.

if this happened after TB auto-updated, then read various options are mentioned here.

some common & new settings are shown here.

Modified by atErik

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Thanks. I prefer not to disable AV software. However, this morning I found a way around it by saving "Sent" messages in a local folder. That doesn't solve the problem between TB and AV software, but it lets me send messages without various intermittent errors that included sending several copies of the same message, not being able to send messages, not being able to set up the account after deleting it.

I went to Settings for the account, chose "Copies and Folders", When sending messages Place a Copy in Other, and selected a previously created local "Sent" folder.

Thank you for your reply. I may not have solved the software conflict, but I can now 1) send messages from the account and 2) have emails scanned for viruses.

Modified by cbrown4

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I can send emails from the account, but not receive them on the W10 computer. I don't understand your AV instructions. I use Avast, and the only option seems to be to turn off email protection, which seems unwise on a windows machine.

linux machines work perfectly. Perhaps there is a problem with windows defender?

Modified by cbrown4

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This worked.

Change Connection security: None. (Tools->Account Settings->Server Settings->Security Settings)

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Security:"None" <- means , NO ENCRYPTION , means NO SECURITY , means DATA IS OPEN , means ANYONE CAN SEE+COPY ANY DATA.


you MUST use something else SECURITY. and also you MUST change PASSWORD, as its EXPOSED , because you've used Security:"None".

please spend time & read the links i posted, try to understand different possible settings, and try them, but do not use Security:"None".

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Chosen Solution

Thank you for your help and concern. With this information, it seems that the easiest solution will be to move to another email client.