Had Google trying to send me mails to non-existing mail-addresses over months. You would think their logs might catch something like that or they would react to my complaints ... they don't and they just dont care.

It sometimes stops for weeks, then it continiues.

from my logs as an example: Nov 13 22:10:51 bert postfix/smtpd[2693931]: NOQUEUE: reject: RCPT from mail-oi1-x248.google.com[2607:f8b0:4864:20::248]: 450 4.1.8 <ki+bncBD77RLFFQACRBZOX3DEAMGQEU5V3LXY@zf.thesparklebar.com>: Sender address rejected: Domain not found; from=<ki+bncBD77RLFFQACRBZOX3DEAMGQEU5V3LXY@zf.thesparklebar.com> to=<rmayer13@nerd-residenz.de> proto=ESMTP helo=<mail-oi1-x248.google.com> Nov 13 22:12:07 bert postfix/smtpd[2696594]: NOQUEUE: reject: RCPT from mail-ua1-x948.google.com[2607:f8b0:4864:20::948]: 450 4.1.8 <ki+bncBD77RLFFQACRBZOX3DEAMGQEU5V3LXY@zf.thesparklebar.com>: Sender address rejected: Domain not found; from=<ki+bncBD77RLFFQACRBZOX3DEAMGQEU5V3LXY@zf.thesparklebar.com> to=<rmayer1000@nerd-residenz.de> proto=ESMTP helo=<mail-ua1-x948.google.com> Nov 13 22:12:18 bert postfix/smtpd[2696594]: NOQUEUE: reject: RCPT from mail-wm1-x346.google.com[2a00:1450:4864:20::346]: 450 4.1.8 <ki+bncBDO2ZDH5DIIOXB6ZZADBUBFIYC6HQ@zf.thesparklebar.com>: Sender address rejected: Domain not found; from=<ki+bncBDO2ZDH5DIIOXB6ZZADBUBFIYC6HQ@zf.thesparklebar.com> to=<rmayer13@nerd-residenz.de> proto=ESMTP helo=<mail-wm1-x346.google.com> Nov 13 22:12:37 bert postfix/smtpd[2696594]: NOQUEUE: reject: RCPT from mail-lf1-x146.google.com[2a00:1450:4864:20::146]: 450 4.1.8 <ki+bncBDO2ZDH5DIIOXB6ZZADBUBFIYC6HQ@zf.thesparklebar.com>: Sender address rejected: Domain not found; from=<ki+bncBDO2ZDH5DIIOXB6ZZADBUBFIYC6HQ@zf.thesparklebar.com> to=<rmayer333@nerd-residenz.de> proto=ESMTP helo=<mail-lf1-x146.google.com> Nov 13 22:13:08 bert postfix/smtpd[2696594]: NOQUEUE: reject: RCPT from mail-lj1-x248.google.com[2a00:1450:4864:20::248]: 450 4.1.8 <hc+bncBDO2ZDH5DIIOXB6ZZADBUBB2QEZ74@zf.thesparklebar.com>: Sender address rejected: Domain not found; from=<hc+bncBDO2ZDH5DIIOXB6ZZADBUBB2QEZ74@zf.thesparklebar.com> to=<rmayer@nerd-residenz.de> proto=ESMTP helo=<mail-lj1-x248.google.com> Nov 13 22:13:08 bert postfix/smtpd[2696594]: NOQUEUE: reject: RCPT from mail-wm1-x345.google.com[2a00:1450:4864:20::345]: 450 4.1.8 <ki+bncBDO2ZDH5DIIOXB6ZZADBUBFIYC6HQ@zf.thesparklebar.com>: Sender address rejected: Domain not found; from=<ki+bncBDO2ZDH5DIIOXB6ZZADBUBFIYC6HQ@zf.thesparklebar.com> to=<rmayerrmayer@nerd-residenz.de> proto=ESMTP helo=<mail-wm1-x345.google.com> Nov 13 22:14:03 bert postfix/smtpd[2696594]: NOQUEUE: reject: RCPT from mail-lj1-x248.google.com[2a00:1450:4864:20::248]: 450 4.1.8 <ki+bncBDO2ZDH5DIIOXB6ZZADBUBFIYC6HQ@zf.thesparklebar.com>: Sender address rejected: Domain not found; from=<ki+bncBDO2ZDH5DIIOXB6ZZADBUBFIYC6HQ@zf.thesparklebar.com> to=<rmayera@nerd-residenz.de> proto=ESMTP helo=<mail-lj1-x248.google.com>

As you can see, the to-address is generated and its different hosts at google trying to send mails.

Searching for zf.thesparklebar.com shows others having the same problem.

Not an expert, but AFAIK 450 is a non-permanent error that basically says "try again later".