Postmark

Great app by the P&T team - as always! Postmark itself is also a good option and a great substitute for SendGrid - since their recent agressive pricing model restructure became unsuitable for the lightweight users (ie. those just looking to increase deliverability). Happy with the switch to Postmark and well supported in the Craft environment thanks to this app.

Does exactly what it needs to do, clean, simple, quick to set up.