Problem with sending email from gmail (as smtp client)

[sce]

Hey guys! I have myself another snafu.

I have a gmail account and I use it to send emails also from "work" email (basically as smtp client) but I have a problem as it won't send emails. Its called "Send mail as" (not alias). The log in /var/log/rejectlog I see this:

2020-09-29 10:52:02 H=mail-qk1-f174.google.com [209.85.222.174] X=TLS1.2:ECDHE-RSA-AES128-GCM-SHA256:128 CV=no F=<[email protected]> A=plain:[email protected] rejected RCPT <[email protected]>:

The problem I have is that there is no msg why, so I cant even diagnose this. Any Idea what to test out?

 

[floyd]

rejected RCPT <[email protected]>:[/I]

There is your message. You have to find out why that email is being rejected.

 

[sce]

I thought that problem was on my end. Hm. So I have to contact client's provider (well i created a test email on their domain, on their shared hosting. I do not have more access than basic cpanel.)? Can you confirm this?