Why bother, it is just simple HTML, isn't it? What can possibly go wrong?
The best reason I heard, when starting working with e-mails, was from a colleague:
'You can not change an e-mail once it is sent out!'
On the one side it is the visual impression, there the difficulty is in the wide range of display options and interpretation by devices, clients, providers.
On the other side there is the complexity of the content - the one static content for everybody, like some marketing where every recipient gets the same,
or some customised dynamic, like just a summary of your last weeks actions on a social network or an invoice, with text + HTML version + PDF as attachment.
And it doesn't stop with the content, there is also the question how to get the e-mail to the recipient?
When you write an e-mail on your computer, you hit the send button in your client, then you assume it is done.
But if you need to send out Millions of e-mails, you need to be sure they are send out fast, there is the next trap:
(Sending out e-mails 'fast' is a technical issue, usually solved by enough servers or by your need: How fast is fast enough?)
Every major domain watches you, your sending servers, you can get easily banned by them for sending out spammy e-mails or too much e-mails
in a short timeframe - then in the most worst case no e-mail will reach a recipient with that domain, or at least with a delay, which is bad in case of registration or password reset e-mails.
How to recognise that?
What to do about that?
Once the e-mail is read by the recipient, our questions go on: How to verify the e-mail got received?
How well received is the e-mail by the recipient. What is the goal of your e-mail? Do you want to make the user to click?
Is it just informal? Does the user take a look onto the e-mail at all?
How to find out?
List of all parts:
Next part will be about the frontend of an e-mail: https://einmanaleiki.de/testing-e-mails-frontend-part-2-31