I find that after using Mail Merge with Attachments, my subsequent email messages are blacklisted and classified spam by Google.

The error message is:

Our system has detected that this message is 421-4.7.0 suspicious due to the nature of the content and/or the links within.

This can appear even when there are no links in the email.

I have been using the add-on only to email existing contacts about current business.

But is there any way it might be triggering action from Google?

Thanks.