Issue Summary

Emails containing specific content cannot be send using SG, due to content validation.

I cannot find any documentation of this "feature".

Please narrow validation and document it or remove it at all.

Steps to Reproduce

1. Try to send email with following content: SG..

Result:
IllegalArgumentException: Found a Forbidden Pattern in the content of the email

Technical details:

This error it because of content validation using regexp .*SG\.[a-zA-Z0-9(-|_)]*\.[a-zA-Z0-9(-|_)]*.*, which is so wide. AFAIU this is to prevent leakage of SG API KEYs, but it block legal content to be sent.