As shared hosting environments become increasing more strict about emails, flagging perfectly legitimate emails to customers as spam, can anyone recommend an email service for transactional email? If anyone has tried these services what were your experiences?

hello, 

With the spam, some verification is made, if you want to have the best rate for your email, it's better do not use the newsletter and to export in tool make for that.

after if you are on dedicated serer, it's important to include inside your dns fkim and spdf (If i remember).

The conversation with your customer must be in function the need and their agreement.

You must be carefull at this :

 

Excessive volume of emails (exceeding host's per-minute, per-hour, per-day caps). You need to find out from your host what the limits are (important for newsletter).
Newsletters and other "not necessary" communications (mass mailings) have to be explicitly "opt in", to avoid legal problems and accusations of spamming.

Respect the regulation and if the customer has opt in the newsletter.

If your host (or other systems, such as Yahoo or Gmail) are flagging the content of any of your emails as spam, you will need to adjust the wording and contents to pass the spam tests.

I agree with @Foster, I have been some clients with a problem with that. Lost an email could be not good for the business.