They have a lot of positive points, but I can give a few negatives to try to balance out the opinions:
* When sending emails to others, in my experience they usually arrive at spam. This could be because in those cases I was sending from domains less than one year old, but I don't think I've had this issue with other providers (e.g. Protonmail).
* Using them to send emails in any automated way (e.g. scripting) is against their TOS. I understand their reasoning, but I would have liked this rule to be relaxed a bit because I would really like to use it for sending notifications to myself, so I would be happy even with a restriction like "if sender and receiver are the same address (or part of the same mailbox), you're allowed to use scripts to send those".
* They don't guarantee any kind of SLA. If they go down, they go down. Not a problem most of the time, but during the start of The Pandemic they had a lot of downtime and that made me realize how painful it is to try to use email when the provider has flaky availability. They fixed it after ~3 months or so, but that was bad enough to make me stop using them for some time. When I heard they fixed it I gave them a second chance and haven't had any issues since then (it's been 3-4 years already and I haven't noticed issues). But this single experience is hard to forget, so I don't use them for anything critical (stuff I would need to read in less than 24 hours or so, much less respond), just in case. Even if SMTP should mostly ensure that you eventually receive emails, and that your sent emails eventually reach their destination, I still have the critical stuff sent to a Gmail or Outlook address.
Despite those points, I like their service enough that I still recommend them from time to time.
I've been using them for years and did not realize they don't allow automated emails. At some point I was sending some automated emails from one inbox to another, but they were very infrequent, less than 1 a day. If you're looking for email-based notifications, I'd recommend Pushover [0] anyways. It's more flexible (can do email, curl, etc.), free, and won't violate ToS.
They have a lot of positive points, but I can give a few negatives to try to balance out the opinions:
* When sending emails to others, in my experience they usually arrive at spam. This could be because in those cases I was sending from domains less than one year old, but I don't think I've had this issue with other providers (e.g. Protonmail).
* Using them to send emails in any automated way (e.g. scripting) is against their TOS. I understand their reasoning, but I would have liked this rule to be relaxed a bit because I would really like to use it for sending notifications to myself, so I would be happy even with a restriction like "if sender and receiver are the same address (or part of the same mailbox), you're allowed to use scripts to send those".
* They don't guarantee any kind of SLA. If they go down, they go down. Not a problem most of the time, but during the start of The Pandemic they had a lot of downtime and that made me realize how painful it is to try to use email when the provider has flaky availability. They fixed it after ~3 months or so, but that was bad enough to make me stop using them for some time. When I heard they fixed it I gave them a second chance and haven't had any issues since then (it's been 3-4 years already and I haven't noticed issues). But this single experience is hard to forget, so I don't use them for anything critical (stuff I would need to read in less than 24 hours or so, much less respond), just in case. Even if SMTP should mostly ensure that you eventually receive emails, and that your sent emails eventually reach their destination, I still have the critical stuff sent to a Gmail or Outlook address.
Despite those points, I like their service enough that I still recommend them from time to time.