Gmail: 550 Too many invalid recipients - why and how to fix it?

Question

gmail

I correspond with a person from a box on gmail, everything is fine. Several messages passed in both directions. The person asks to send a Word document, I press reply, I attach the document (it weighs several tens of kilobytes), a chipper comes.
Address not found
Your message wasn't delivered to [email protected] because the address couldn't be found or is unable to receive email.

550 Too many invalid recipients

Why?

The recipient is one. And I have never been a spammer, if suddenly someone had such a hypothesis.

Answer 1

If the mail is corporate, you can configure it as you like, for example, so that the mail server does not accept letters with attachments or with the word spade in the text.
You can also check if they have changed something and the mail has flown. After this error, did you try to send a regular letter without attachments?
Alternatively, try sending the attachment as a link to Google Drive

Answer 2

Here is your reason:

address not found

Offhand, there are several options:

1. Incorrect configuration of the receiving server or temporary failure.
   
2. This person no longer works for this company or has changed address.
   
3. You have been blacklisted, but they do not want to show it explicitly.