Support Sendgrid Personalizations

[cbrewster]

I need to be able to send out newsletters to a list of users. I would like to be able to use the same template and fill in info with substitutions on a per-user basis. Other users also should not be able to see the other recipients of the email in the to field. (See https://sendgrid.com/docs/for-developers/sending-email/personalizations/#sending-two-different-emails-to-two-different-groups-of-recipients)

From looking at the SendGrid adapter, it looks like it hardcodes a single personalization entry. It would be nice if I could add multiple personalization entries for each user and be able to send out the newsletter with a single SendGrid API call.

I am happy to actually implement this, I just want to make sure I am starting in the right direction.

[maymillerricci]

@cbrewster Thanks for posting! This makes sense, and we would welcome a PR for it!

[dantswain]

I would also like this feature. I am willing to do a PR if I can get some indication that it will get attention - it's a little vague if this repo is getting active maintenance or not (see #515)

[maymillerricci]

@dantswain We would welcome a PR for this. Thanks!