Q:

"Unsubscribe" for email categories/types through Sendgrid, Mailchimp, SES

I've got a Rails 3.2 app that will need to send various transactional & bulk (marketing) types of emails. Ideally I'd be able to use a service (like Sendgrid or Amazon SES) to improve deliverability and for unsubscribe support. I've mostly used Sendgrid in the past, but I need the 'unsubscribe' to be just for a specific category of the email (there are around 6 categories). I can't have someone unsubscribing from a marketing email and miss out on notification or invitation emails. Does anyone know of an service that supports this, or does this just have to be done internally? It seems like there's a lot to deal with related to best practices for deliverability, list-unsubscribe, etc. if you manage it yourself. 
I see this discussion on sendgrid, but seems to be pending still:
http://community.sendgrid.com/sendgrid/topics/unsubscribe_and_categories
I'm happy to go with any service if it integrates relatively easily with Rails and can support category/type based subscription management. Or perhaps a hybrid approach with different services or separate accounts on the same service, if they allow that for the same domain? 
I very much appreciate any feedback on how others have tackled this.
Thanks! 

A:

It looks like CritSend(1) have what they call "tag" support and state the following on their site:

Our unsub processing is done per tag, so if someone unsubscribes from
one of your emails tagged "newsletter1" that does not unsubscribe them
from any other tag.

The one thing that is unclear is the level of Ruby support.
CritSend name MxmConnect as the gem to use for sending emails. There is a critsend_events gem for the CritSend Events API.
(1) Note, I have no affiliation with CritSend

