SendGrid

Pros

1. Have AB Testing enable.
2. Manage unsubscribe emails.
3. Easy to Integrate via API or SMTP.
4. Email Reputation indicator.
5.Full detailed report. You can see if the email it's blocked, bounced or delivered.
6. Have a Forever Free plan . (40.000 Emails in the trial period, then 100 Emails Daily forever)

Cons

Send grid interface it's a little bit confuse.

No more cons to highlight, for me it's a perfect tool.

Pros

1. On the bottom left side of the dashboard is a small reputation percentage bar, that measures your reputation. The bar is updated daily based on your email sends, your reputation goes down if your email bounces or is marked as spam.
2. Stats: SendGrid provides A LOT of data on the performance of your email campaigns, these stats are: Requests, Delivered, Opens, Unique Opens, Clicks, Unique Clicks, Unsubscribes, Spam Reports, Bounces, Blocks, Bounce Drops, Spam Report Drops, Unsubscribe Drops and Invalid Emails. SendGrid also provides stats such as: Global Stats, Category Stats, Category Comparison, Subuser Stats, Subuser Comparison, Geographical, Email Clients & Devices, Mailbox Provider Stats, Mailbox Provider Comparison, Browser Stats, and Browser Comparison
3. A/B Testing
4. Unsubscribe Groups: This is without doubt my favorite feature from SendGrid. When you click on "Marketing" on the left side of your dashboard, and select tour from the drop down, it sort of lists steps to set up for sending marketing emails. Step 3 on the list of things to do is to create unsubscribe groups. Here you can Create groups that represent types of email that you regularly send to your recipients. If a recipient chooses to unsubscribe, they will have the option of selecting which of these groups they want to unsubscribe from.

Cons

1. The Email templates in SendGrids gallery are a bit basic which initially wasn't a problem as I liked creating my own template, but I did not like how I couldn't modify the "columns" module to my taste.

I wanted to create a template with three columns with the center column bigger than the two on the side. The idea was to have my client's images linking to their projects (On their websites) on the side columns, with the write up in the center column.
However, that couldn't be done (At least so far it seems so as I can't find any option to tweak the size/width of each column) as each column has an equal width.

2. No automation function: I'd like to create a sort of If/Then sequence where I can resend an email to a group of people after x days, for example, I'd like to resend an email (With a different heading of course) to people who have not opened the first email after four days.

Pros

We use SendGrid for transactional emails, such as welcome messages & notifications. Generally, SendGrid offers great tools to integrate emails into a variety of different application platforms and programming languages. We really like its level of detail when checking on the status of emails. Sendgrid is also free for basic transactional emails, which makes it easy to try and ensure it will work with your application. We use a third-party library called Nodemailer with Sendgrid, so switching from a different service to Sendgrid was trivial.

Cons

While the service is easy to use and offers comprehensive email activity metrics, there are a few things about it we didn't like. First, because the free tier uses shared IPs, we consistently had emails that wouldn't get delivered because of IP blocks. There were a handful of IPs that we had that experience with, and it persisted for weeks -- without any support intervention. Sendgrid must have deliverability metrics on their side as well, so I am surprised they didn't drop these IPs from their IP pool proactively. We had to upgrade to the PRO plan, which was the least expensive plan that had a dedicated IP. We also had to pay extra for 30 days of email history, you get 3 days by default. I'd love to see all these options be a-la-carte, but I get that you need to make revenue somehow, and few companies send enough emails to justify jumping to the next paid plan -- unless you NEED that deliverability guarantee that you get w/ dedicated IPs, which we did.

Pros

Sendgrid is ready for your scale. From the smallest Saas apps to the largest enterprises, Sendgrid was built with scale in mind. It handles transactional emails very well, and is relatively simple to integrate into your codebase or product workflow. Templates come out of the box, but some coding knowledge is needed to style transactional emails. All templates can be easily versioned.

Concerns on security and blacklisting are limited. As long as you follow their recommendations, Sendgrid will deliver your email.

Pricing is very fair and generous. In years of use, I've never gone over a plan limit.

Cons

Functionality can be limited in interesting ways depending on your plan. On the most basic paid plans, several code features are just missing. Reporting is the most glaring issue, with basic reporting showing only a rolling group of recently sent emails. Without a deeper dive into your logs, you may miss issues.

Transactional emails also lack some features that seem required, like weblinks for email and easy native unsubscribe. There are workarounds for both, but not without challenges. Version tracking for templates is also completely missing, unless you use new versions for each edit you make.

Pros

I've used SendGrid for years. They have a 1-click "provision" feature inside the Heroku app store that starts at $0 /month until you hit profit-worthy volume (10k+ emails /month).

The API for sending transactional emails is great, however I have not tried their email marketing feature.

I'm such a big SendGrid fan, in fact, that I built a free SendGrid analytics tool that generates reports for other customers (+ myself) to send better transactional emails: https://lesstransactional.com.

Cons

While building our free SendGrid analytics tool, it became apparent that the "Email Activity" API has a much lower rate limit (ie 10 requests per 5 minutes) than the regular sending APIs.

This required us to make restrictive changes to the app at the last minute, and their support team was unwilling to increase the rate limit for our use case.