[ChipAHoy]

My GMX credentials are fine, I have my full GMX email listed in the Calibre preferences. I looked online and could not find a solution that works for me. Using a Mac here.

None of the mobi files I email to my Kindle show up, when sending them within Calibre. This has worked in the past successfully, and I have not changed any settings within GMX.

Spoiler:

Starting job: Email SLEEPING GIANTS to chip92114pw@kindle.com
Waiting 301 seconds before sending, to avoid being marked as spam.
You can control this delay via Preferences->Tweaks
connect: (u'mail.gmx.com', 587)
connect: (u'mail.gmx.com', 587)
reply: '220 gmx.com (mrgmx102) Nemesis ESMTP Service ready\r\n'
reply: retcode (220); Msg: gmx.com (mrgmx102) Nemesis ESMTP Service ready
connect: gmx.com (mrgmx102) Nemesis ESMTP Service ready
send: 'ehlo Christophers-MacBook-Air.local\r\n'
reply: '250-gmx.com Hello Christophers-MacBook-Air.local [174.65.19.96]\r\n'
reply: '250-AUTH LOGIN PLAIN\r\n'
reply: '250-SIZE 69920427\r\n'
reply: '250 STARTTLS\r\n'
reply: retcode (250); Msg: gmx.com Hello Christophers-MacBook-Air.local [174.65.19.96]
AUTH LOGIN PLAIN
SIZE 69920427
STARTTLS
send: 'STARTTLS\r\n'
reply: '220 OK\r\n'
reply: retcode (220); Msg: OK
send: 'ehlo Christophers-MacBook-Air.local\r\n'
reply: '250-gmx.com Hello Christophers-MacBook-Air.local [174.65.19.96]\r\n'
reply: '250-AUTH LOGIN PLAIN\r\n'
reply: '250 SIZE 69920427\r\n'
reply: retcode (250); Msg: gmx.com Hello Christophers-MacBook-Air.local [174.65.19.96]
AUTH LOGIN PLAIN
SIZE 69920427
send: AUTH <censored>
reply: '535 Authentication credentials invalid\r\n'
reply: retcode (535); Msg: Authentication credentials invalid

Sending failed...

Traceback (most recent call last):
File "site-packages/calibre/gui2/email.py", line 44, in run
File "site-packages/calibre/gui2/email.py", line 134, in sendmail
File "site-packages/calibre/utils/smtp.py", line 154, in sendmail
File "site-packages/calibre/utils/smtplib.py", line 647, in login
SMTPAuthenticationError: (535, 'Authentication credentials invalid')


Retrying in 301 seconds...

Waiting 301 seconds before sending, to avoid being marked as spam.
You can control this delay via Preferences->Tweaks
connect: (u'mail.gmx.com', 587)
connect: (u'mail.gmx.com', 587)
reply: '220 gmx.com (mrgmx101) Nemesis ESMTP Service ready\r\n'
reply: retcode (220); Msg: gmx.com (mrgmx101) Nemesis ESMTP Service ready
connect: gmx.com (mrgmx101) Nemesis ESMTP Service ready
send: 'ehlo Christophers-MacBook-Air.local\r\n'
reply: '250-gmx.com Hello Christophers-MacBook-Air.local [174.65.19.96]\r\n'
reply: '250-AUTH LOGIN PLAIN\r\n'
reply: '250-SIZE 69920427\r\n'
reply: '250 STARTTLS\r\n'
reply: retcode (250); Msg: gmx.com Hello Christophers-MacBook-Air.local [174.65.19.96]
AUTH LOGIN PLAIN
SIZE 69920427
STARTTLS
send: 'STARTTLS\r\n'
reply: '220 OK\r\n'
reply: retcode (220); Msg: OK
send: 'ehlo Christophers-MacBook-Air.local\r\n'
reply: '250-gmx.com Hello Christophers-MacBook-Air.local [174.65.19.96]\r\n'
reply: '250-AUTH LOGIN PLAIN\r\n'
reply: '250 SIZE 69920427\r\n'
reply: retcode (250); Msg: gmx.com Hello Christophers-MacBook-Air.local [174.65.19.96]
AUTH LOGIN PLAIN
SIZE 69920427
send: AUTH <censored>
reply: '535 Authentication credentials invalid\r\n'
reply: retcode (535); Msg: Authentication credentials invalid

Sending failed...

Traceback (most recent call last):
File "site-packages/calibre/gui2/email.py", line 44, in run
File "site-packages/calibre/gui2/email.py", line 134, in sendmail
File "site-packages/calibre/utils/smtp.py", line 154, in sendmail
File "site-packages/calibre/utils/smtplib.py", line 647, in login
SMTPAuthenticationError: (535, 'Authentication credentials invalid')

Job: "Email SLEEPING GIANTS to chip92114pw@kindle.com" failed with error:
Traceback (most recent call last):
File "site-packages/calibre/gui2/threaded_jobs.py", line 84, in start_work
File "site-packages/calibre/gui2/email.py", line 101, in __call__
SMTPAuthenticationError: (535, 'Authentication credentials invalid')

Called with args: (u'/var/folders/p3/tr15nn4x7wd4ghvg_hs4zslr0000gn/C/calibre_3.25.0_tmp_wgCFPT/IOr4_3caltmpfmt.mobi', u'SLEEPING GIANTS - Sylvain Neuvel.mobi', u'chip92114pw@kindle.com', 'EMAIL', u'Attached, you will find the e-book\n\nSLEEPING GIANTS\n\tby Sylvain Neuvel\n\nin the MOBI format.') {u'log': <calibre.utils.logging.GUILog object at 0x1259b4050>, u'abort': <threading._Event object at 0x11c3f8e10>, u'notifications': <Queue.Queue instance at 0x1259b2bd8>}