If this was in a formal business email, I would say it's grammatical but overly casual. As you well know, the ています-to-てます-conversion is very common in casual and colloquial Japanese, but that's not something you can use in a business email.
They should have wrote in one of the followings ways:
- 搭載されております機能 (using humble おる)
As you can see, using ます to modify the following noun like this is not uncommon.
That said, the last one is universally valid, and I personally prefer it even in a formal email. There is no need to use 丁寧語 there, and I feel that using the first form too much may leave an obsequious impression on people.
Of course you can safely say "搭載されてる機能" in a casual situation.