Why BikeGremlin doesn't accept temp-email user registrations

[BikeGremlin]

No temporary or "+" emails allowed? Why?
For anonymity, you can use the free Proton mail.
I’ll do my best to provide a comprehensive answer, understandable even for those "not in the field". I'll use my own domain ("Bikegremlin", "my server", etc.) as an example, but almost everything written here applies generally.

Domain reputation​

BikeGremlin doesn’t send spam (this applies to both the bikegremlin.com website and the bikegremlin.net forum).

Every forum user can turn off any email notification (or all of them) in their account options.

I don’t send mass emails (commonly known as "newsletters") - except in truly exceptional situations.
No adverts or anything like that. I follow this principle:
If it’s not important enough to call a friend about, then I won’t send it to subscribers by email. I may have sent a total of five newsletters in the last ten years.

Thanks to a good ten-year history, BikeGremlin domain has an excellent email sending reputation (the best possible for a private domain not owned by a large corporation - I’m not at Google’s level yet ).

I strive to maintain that.

The problem with temporary ("throwaway") emails​

Temporary emails, as their name suggests, have a limited lifespan (sometimes less than a month). This creates a problem for three reasons/scenarios:

1) Receiving notifications
If a user’s email is no longer available, any emails sent to that address will bounce. This prevents contact and damages the sending domain’s reputation (i.e, the bikegremlin.net domain in this case).

2) Forgotten password
If a user forgets their password, I don’t want to know the user’s new password - I want it to remain private, even from me (passwords are encrypted on the server). The way to reset a password is for the user to request a temporary link to be sent to their email, which would allow them to set a new password. Of course, this is sent to the email registered when the account was created (otherwise a user could reset someone else’s password).
SPF, DKIM, and DMARC DNS settings for the BikeGremlin domain prevent anyone else from fraudulently sending such an email on behalf of BikeGremlin without it being blocked as spam.

3) High percentage of spam and other malicious activities
Temporary emails (and "permanent" ones from certain domains) are used for spam, phishing links, and other malicious activities. Banning the use of temporary emails helps protect all users through forum administration and the blocking of such content.
This brings us to the next section:

In a separate article, I've explained why using email forwarders can bite you in the back.

What about email addresses with a "+" (plus sign)?​

Plus-addressing is not allowed on the BikeGremlin forum - it helps keep things manageable and fair for everyone. What's that and why is it forbidden?

Many email services (like Gmail, ProtonMail, Fastmail...) allow users to add a + sign and custom text to their address - for example:
"[email protected]". This feature is sometimes used by privacy-conscious users to track who shared or leaked their email. That's perfectly fine when used responsibly. Unfortunately, it's also commonly abused by spammers, bots, and abusers to:

• Bypass bans and register multiple accounts using the same inbox.
• Create dozens or hundreds of fake accounts quickly.
• Hide their real identity while maintaining access to the inbox.

From a spam protection and moderation standpoint, this makes tracking and banning repeat offenders harder (it also makes it harder to track email bounces and similar). If you want to use a separate address for the forum, I recommend creating a real, unique email like:
"[email protected]".

User privacy protection​

• User emails are not publicly visible.
• Users cannot make their email publicly available, even if they want to
  (or, a more likely scenario, if they accidentally click the checkbox to make their email public).

However, to be fair, email addresses are not encrypted, so hacking the forum could give hackers a list of email addresses (account passwords are encrypted though, so they would not be accessible to hackers).

Therefore, it makes sense to use a separate email for forum registrations and the like, but (at least as far as BikeGremlin is concerned) it’s important that this email is real and available (not temporary).

Solution and recommendation?​

Personally, I trust Proton and their private email service, which does not share personal data:
https://proton.me/mail

The service offers 1 GB of storage for free, which is more than enough (email shouldn’t be used for backup or data storage – although a large percentage of people make that mistake, but that’s another topic).

So, this isn’t a temporary email, but a real, permanent one with privacy protection.

Final notes​

I believe privacy protection is important, but that it can be achieved without using temporary emails.

For the reasons given above, I’ve decided not to accept member registrations with temporary emails.

It’s not my goal to have as many people as possible on the forum at any cost, and it’s completely fine if someone chooses not to register because they can’t use a temporary email.

Additional sources and information​

For anyone interested, here are a couple of useful and educational articles:

• Safe email handling habits
• Why SPF, DKIM, and DMARC DNS settings are important for preventing phishing

Relja