Sendgrid is the largest player in the transactional email market, with customers like Pinterest, Spotify and FourSquare.
Pro Both newsletter and transactional emails
Usually when choosing a service to send your application's emails you need two. One to send the newsletter or news and promotions from the marketing team and the other to send you application's automatic emails and messages.
With SendGrid you don't have to choose two because it doubles both as a transactional and marketing platform at once.
Pro Great support for beginners and experienced users
If you are just getting started with email marketing and transactional emails or if you get stuck somewhere, SendGrid includes amazing videos and guides to help you work out any problem you may have. What's more, it also has phone, chat and email support available 24/7.
Con Not suitable for people without a technical background
There are some features which are missing by default from SendGrid (sign-up forms or follow-up messages just to name a few). In order to implement those in your emails, you need to know how to program because you have to code them yourself through SendGrid's API.
Con Port 2525 is not encrypted
Most cloud providers block ports 25, 465, and 587. Port 2525 is commonly open but SendGrid only allows unencrypted messages via that port.
Note: There are also so some certificate issues (see https://support.sendgrid.com/hc/en-us/articles/200182008-Certificate-verification-failed-for-smtp-sendgrid-net)
Con No sandbox/test mode
Does not support test keys that can be used to check integration with SendGrid and that cannot be used to send real e-mail out. It means that either you don't cannot verify that your integration with SendGrid works during development, or you have to use real credentials which should not be shared widely across your team.