Are emails sent from a Google mailbox going to spam or am I blacklisted?

Question

gmail

Friends!
I need your help!
For two years now I have been using Google mail, tied to my domain. Never had a problem. I tied it myself, clearly according to the Google instructions. This week I noticed the following:
1. Tried to reply to a letter from a foreign colleague, received:
Delivery to the following recipient failed permanently: [email protected]
Technical
details of permanent failure:
Google tried to deliver your message, but it was rejected by the server for the recipient domain by mta1b.mail.zscaler.net. [209.51.184.16].
The error that the other server returned was:
550 Mailbox denied: No access
2. I tried to find out the details of the apartment reservation from the Spaniards, I got:
Delivery to the following recipient failed permanently:
[email protected]
Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the server for the recipient domain apartescor.com by creac-sf.creactivitat.com. [62.97.115.39].
3. Wrote a letter to a friend on google mail (the standard name is gmail .com), got into the spam folder.
The question is what to do? What could be the problem? Poke your nose.
Thank you!