I have some Gmail Business account set in Thunderbird (91.6 version). Randomly, when they send an email, it appears the sending bar that hangs until they clic on cancel icon. After that appears the window "Sending the message failed. Authentication not with outgoing server (SMTP) smtp.gmail.com. Check the password and verify the "Authentication Method" in Account Settings | Outgoing mail server (SMTP)". If I close and reopen Thunderbird it works properly and sends the email for many hours The SMTP server settings are: Server Name: smtp.gmail.com Port: 465 Connection: SSL Authentication: OAuth2 In the file log I found this error: 2022-02-11 09:13:26.813000 UTC - [Parent 9496: IMAP]: D/IMAP SetConnectionStatus(0x0) 2022-02-11 09:13:26.813000 UTC - [Parent 9496: IMAP]: D/IMAP Try to log in 2022-02-11 09:13:26.813000 UTC - [Parent 9496: IMAP]: D/IMAP IMAP auth: server caps 0xc080c1625, pref 0x800000000, failed 0x0, avail caps 0x800000000 2022-02-11 09:13:26.813000 UTC - [Parent 9496: IMAP]: D/IMAP (GSSAPI = 0x1000000, CRAM = 0x20000, NTLM = 0x100000, MSN = 0x200000, PLAIN = 0x1000, LOGIN = 0x2, old-style IMAP login = 0x4, auth external IMAP login = 0x20000000, OAUTH2 = 0x800000000) 2022-02-11 09:13:26.813000 UTC - [Parent 9496: IMAP]: D/IMAP Trying auth method 0x800000000 2022-02-11 09:13:26.813000 UTC - [Parent 9496: IMAP]: D/IMAP IMAP: trying auth method 0x800000000 2022-02-11 09:13:26.813000 UTC - [Parent 9496: IMAP]: D/IMAP XOAUTH2 auth 2022-02-11 09:13:26.879000 UTC - [Parent 9496: IMAP]: D/IMAP OAuth2 failed 2022-02-11 09:13:26.879000 UTC - [Parent 9496: IMAP]: D/IMAP authlogin failed 2022-02-11 09:13:26.879000 UTC - [Parent 9496: IMAP]: D/IMAP Marking auth method 0x800000000 failed 2022-02-11 09:13:26.879000 UTC - [Parent 9496: IMAP]: D/IMAP IMAP auth: server caps 0xc080c1625, pref 0x800000000, failed 0x800000000, avail caps 0x0 2022-02-11 09:13:26.879000 UTC - [Parent 9496: IMAP]: D/IMAP (GSSAPI = 0x1000000, CRAM = 0x20000, NTLM = 0x100000, MSN = 0x200000, PLAIN = 0x1000, LOGIN = 0x2, old-style IMAP login = 0x4, auth external IMAP login = 0x20000000, OAUTH2 = 0x800000000) 2022-02-11 09:13:26.879000 UTC - [Parent 9496: IMAP]: D/IMAP No remaining auth method 2022-02-11 09:13:26.879000 UTC - [Parent 9496: IMAP]: E/IMAP login failed entirely 2022-02-11 09:13:26.879000 UTC - [Parent 9496: IMAP]: D/IMAP SetConnectionStatus(0x80004005) 2022-02-11 09:13:26.879000 UTC - [Parent 9496: IMAP]: D/IMAP URL failed with code 0x80004005 (imap://USERNAME%40DOMAIN%[email protected]:993/appenddraftfromfile%3E/%5BGmail%5D/Bozze%3EUID%3E) 2022-02-11 09:13:26.879000 UTC - [Parent 9496: IMAP]: I/IMAP 23e9568e800:imap.gmail.com:NA:ProcessCurrentURL: aborting queued urls 2022-02-11 09:13:26.879000 UTC - [Parent 9496: IMAP]: I/IMAP 23e9568e800:imap.gmail.com:NA:TellThreadToDie: close socket connection 2022-02-11 09:13:26.879000 UTC - [Parent 9496: IMAP]: D/IMAP ImapThreadMainLoop leaving [this=23e9568e800] 2022-02-11 09:14:19.331000 UTC - [Parent 9496: IMAP]: D/IMAP ReadNextLine [rv=0x0 stream=23e9ad62e50 nb=17 needmore=0] I already created a new profile, deleting all the password saved, disabled index and copy message to the folder..... I also clean cache and disable proxy connection. Thank you for your support