[painting-words]

Sorry for highjacking this post, I've just had a similar problem for ages and taking a chance that someone knows how to help me... I've been unable to use the send email to kindle function for ages now.
If that's relevant, I run calibre 5.44 because my Mac iOS is too old... and I have a @hotmail.com address.

Anyway, just in case, here's the error message I got when I tried today:

Spoiler:

calibre, version 5.44.0 (darwin, embedded-python: True)
Failed to email book: Failed: Email NAME OF BOOK to myaccount@kindle.com

Starting job: Email NAME OF BOOK to myaccount@kindle.com
Waiting 301 seconds before sending, to avoid being marked as spam.
You can control this delay via Preferences->Tweaks
connect: ('smtp-mail.outlook.com', 587)
connect: to ('smtp-mail.outlook.com', 587) None
reply: b'220 YQZPR01CA0089.outlook.office365.com Microsoft ESMTP MAIL Service ready at Fri, 5 Jan 2024 21:18:34 +0000\r\n'
reply: retcode (220); Msg: b'YQZPR01CA0089.outlook.office365.com Microsoft ESMTP MAIL Service ready at Fri, 5 Jan 2024 21:18:34 +0000'
connect: b'YQZPR01CA0089.outlook.office365.com Microsoft ESMTP MAIL Service ready at Fri, 5 Jan 2024 21:18:34 +0000'
send: 'ehlo MacBook-Air-de-myname.local\r\n'
reply: b'250-YQZPR01CA0089.outlook.office365.com Hello [216.137.119.154]\r\n'
reply: b'250-SIZE 157286400\r\n'
reply: b'250-PIPELINING\r\n'
reply: b'250-DSN\r\n'
reply: b'250-ENHANCEDSTATUSCODES\r\n'
reply: b'250-STARTTLS\r\n'
reply: b'250-8BITMIME\r\n'
reply: b'250-BINARYMIME\r\n'
reply: b'250-CHUNKING\r\n'
reply: b'250 SMTPUTF8\r\n'
reply: retcode (250); Msg: b'YQZPR01CA0089.outlook.office365.com Hello [216.137.119.154]\nSIZE 157286400\nPIPELINING\nDSN\nENHANCEDSTATUSCODES\nS TARTTLS\n8BITMIME\nBINARYMIME\nCHUNKING\nSMTPUTF8'
send: 'STARTTLS\r\n'
reply: b'220 2.0.0 SMTP server ready\r\n'
reply: retcode (220); Msg: b'2.0.0 SMTP server ready'
send: 'ehlo MacBook-Air-de-myname.local\r\n'
reply: b'250-YQZPR01CA0089.outlook.office365.com Hello [216.137.119.154]\r\n'
reply: b'250-SIZE 157286400\r\n'
reply: b'250-PIPELINING\r\n'
reply: b'250-DSN\r\n'
reply: b'250-ENHANCEDSTATUSCODES\r\n'
reply: b'250-AUTH LOGIN XOAUTH2\r\n'
reply: b'250-8BITMIME\r\n'
reply: b'250-BINARYMIME\r\n'
reply: b'250-CHUNKING\r\n'
reply: b'250 SMTPUTF8\r\n'
reply: retcode (250); Msg: b'YQZPR01CA0089.outlook.office365.com Hello [216.137.119.154]\nSIZE 157286400\nPIPELINING\nDSN\nENHANCEDSTATUSCODES\nA UTH LOGIN XOAUTH2\n8BITMIME\nBINARYMIME\nCHUNKING\nSMTPUTF8'
send: AUTH <censored>
reply: b'334 UGFzc3dvcmQ6\r\n'
reply: retcode (334); Msg: b'UGFzc3dvcmQ6'
send: 'MjF0b3dsSFRNTDQ=\r\n'
reply: b'535 5.7.139 Authentication unsuccessful, the user credentials were incorrect. [YQZPR01CA0089.CANPRD01.PROD.OUTLOOK.COM 2024-01-05T21:18:46.945Z 08DC0D13B8359358]\r\n'
reply: retcode (535); Msg: b'5.7.139 Authentication unsuccessful, the user credentials were incorrect. [YQZPR01CA0089.CANPRD01.PROD.OUTLOOK.COM 2024-01-05T21:18:46.945Z 08DC0D13B8359358]'

Sending failed...

Traceback (most recent call last):
File "calibre/gui2/email.py", line 48, in run
File "calibre/gui2/email.py", line 137, in sendmail
File "calibre/utils/smtp.py", line 180, in sendmail
File "smtplib.py", line 734, in login
File "smtplib.py", line 723, in login
File "smtplib.py", line 646, in auth
smtplib.SMTPAuthenticationError: (535, b'5.7.139 Authentication unsuccessful, the user credentials were incorrect. [YQZPR01CA0089.CANPRD01.PROD.OUTLOOK.COM 2024-01-05T21:18:46.945Z 08DC0D13B8359358]')


Retrying in 301 seconds...

Waiting 301 seconds before sending, to avoid being marked as spam.
You can control this delay via Preferences->Tweaks
connect: ('smtp-mail.outlook.com', 587)
connect: to ('smtp-mail.outlook.com', 587) None
reply: b'220 YQBPR01CA0098.outlook.office365.com Microsoft ESMTP MAIL Service ready at Fri, 5 Jan 2024 21:23:47 +0000\r\n'
reply: retcode (220); Msg: b'YQBPR01CA0098.outlook.office365.com Microsoft ESMTP MAIL Service ready at Fri, 5 Jan 2024 21:23:47 +0000'
connect: b'YQBPR01CA0098.outlook.office365.com Microsoft ESMTP MAIL Service ready at Fri, 5 Jan 2024 21:23:47 +0000'
send: 'ehlo MacBook-Air-de-myname.local\r\n'
reply: b'250-YQBPR01CA0098.outlook.office365.com Hello [216.137.119.154]\r\n'
reply: b'250-SIZE 157286400\r\n'
reply: b'250-PIPELINING\r\n'
reply: b'250-DSN\r\n'
reply: b'250-ENHANCEDSTATUSCODES\r\n'
reply: b'250-STARTTLS\r\n'
reply: b'250-8BITMIME\r\n'
reply: b'250-BINARYMIME\r\n'
reply: b'250-CHUNKING\r\n'
reply: b'250 SMTPUTF8\r\n'
reply: retcode (250); Msg: b'YQBPR01CA0098.outlook.office365.com Hello [216.137.119.154]\nSIZE 157286400\nPIPELINING\nDSN\nENHANCEDSTATUSCODES\nS TARTTLS\n8BITMIME\nBINARYMIME\nCHUNKING\nSMTPUTF8'
send: 'STARTTLS\r\n'
reply: b'220 2.0.0 SMTP server ready\r\n'
reply: retcode (220); Msg: b'2.0.0 SMTP server ready'
send: 'ehlo MacBook-Air-de-myname.local\r\n'
reply: b'250-YQBPR01CA0098.outlook.office365.com Hello [216.137.119.154]\r\n'
reply: b'250-SIZE 157286400\r\n'
reply: b'250-PIPELINING\r\n'
reply: b'250-DSN\r\n'
reply: b'250-ENHANCEDSTATUSCODES\r\n'
reply: b'250-AUTH LOGIN XOAUTH2\r\n'
reply: b'250-8BITMIME\r\n'
reply: b'250-BINARYMIME\r\n'
reply: b'250-CHUNKING\r\n'
reply: b'250 SMTPUTF8\r\n'
reply: retcode (250); Msg: b'YQBPR01CA0098.outlook.office365.com Hello [216.137.119.154]\nSIZE 157286400\nPIPELINING\nDSN\nENHANCEDSTATUSCODES\nA UTH LOGIN XOAUTH2\n8BITMIME\nBINARYMIME\nCHUNKING\nSMTPUTF8'
send: AUTH <censored>
reply: b'334 UGFzc3dvcmQ6\r\n'
reply: retcode (334); Msg: b'UGFzc3dvcmQ6'
send: 'MjF0b3dsSFRNTDQ=\r\n'
reply: b'535 5.7.139 Authentication unsuccessful, the user credentials were incorrect. [YQBPR01CA0098.CANPRD01.PROD.OUTLOOK.COM 2024-01-05T21:23:59.254Z 08DC0CC9A22E0E4F]\r\n'
reply: retcode (535); Msg: b'5.7.139 Authentication unsuccessful, the user credentials were incorrect. [YQBPR01CA0098.CANPRD01.PROD.OUTLOOK.COM 2024-01-05T21:23:59.254Z 08DC0CC9A22E0E4F]'

Sending failed...

Traceback (most recent call last):
File "calibre/gui2/email.py", line 48, in run
File "calibre/gui2/email.py", line 137, in sendmail
File "calibre/utils/smtp.py", line 180, in sendmail
File "smtplib.py", line 734, in login
File "smtplib.py", line 723, in login
File "smtplib.py", line 646, in auth
smtplib.SMTPAuthenticationError: (535, b'5.7.139 Authentication unsuccessful, the user credentials were incorrect. [YQBPR01CA0098.CANPRD01.PROD.OUTLOOK.COM 2024-01-05T21:23:59.254Z 08DC0CC9A22E0E4F]')

Job: "Email NAME OF BOOK to myaccount@kindle.com" failed with error:
Traceback (most recent call last):
File "calibre/gui2/threaded_jobs.py", line 82, in start_work
File "calibre/gui2/email.py", line 105, in __call__
File "calibre/gui2/email.py", line 48, in run
File "calibre/gui2/email.py", line 137, in sendmail
File "calibre/utils/smtp.py", line 180, in sendmail
File "smtplib.py", line 734, in login
File "smtplib.py", line 723, in login
File "smtplib.py", line 646, in auth
smtplib.SMTPAuthenticationError: (535, b'5.7.139 Authentication unsuccessful, the user credentials were incorrect. [YQBPR01CA0098.CANPRD01.PROD.OUTLOOK.COM 2024-01-05T21:23:59.254Z 08DC0CC9A22E0E4F]')

Called with args: ('/var/folders/hk/ty5tg4x13xxb3m8yzp9rqbg80000gn/C/calibre_5.44.0_tmp_7z9hrhk5/vnx52qabcaltmpfmt.epub', "NAME OF BOOK.epub", 'myaccount@kindle.com', "E-book: NAME OF BOOK", "Attached, you will find the e-book\n\nNAME OF BOOK\n\tby AUTHOR\n\nin the EPUB format.") {'notifications': <queue.Queue object at 0x1230c2910>, 'abort': <threading.Event object at 0x1230c2e50>, 'log': <calibre.utils.logging.GUILog object at 0x1230c2f10>}

If anyone has any idea what's the issue and can point me to a solution, it would be much appreciated!