Reply from Clean EmailSep 9, 2025
Hi there! This is Kyryl, I am the founder of Clean Email and one of the engineers behind it. I happened to design this flow in Clean Email and happy to explain why it works like that.
When designing a flow that will affect millions of people it's important to understand both technical limitations and real-life implications of our choices.
The only way to send emails FROM: the account email is to use account's SMTP to send that email, otherwise SPF and DKIM will not be aligned and delivery of such an email will fail. This approach, however, has a lot of limitations, and two of the most significant ones are:
- Most providers limit the number of emails that can be sent per day, per hour, and per minute. Providers do not disclose those limitations for obvious reasons.
- Lots of "unsubscribe" emails are undeliverable and will result in failed delivery attempts flooding the user's Inbox.
As a result, while using Clean Email, users would've started getting unexpected emails about delivery errors causing confusion and would risk getting their account blocked because the number of outgoing emails would've significantly increased beyond "normal" triggering spam protection of the email provider.
In addition to that, we must remember that there are multiple situations in which the "from" email of an email account is not the email address they subscribed with. A lot of people use:
- "+" sign in their gmail addresses ("[email protected]")
- Apple private relay which obfuscates your address
- Forwarding (sometimes multiple mailboxes forward into one account)
In all of these situations sending an email "from:" the current account will not be recognized by the unsubscribe process of the mailing list because the original email is different from the "from:" field.
Additionally, the RFC spec for List-Unsubscribe does not require an unsubscribe email to be sent from the subscribing mailbox. Instead, it is suggested that both one-click unsubscribe URLs and mailto: values contain unique identifiers of the subscription to avoid the issues described above. Placing the email in the body is an accepted (albeit not officially documented or required) way of providing additional context to the mailing list.
Realistically though, mailing list providers responsible for ~99% of list-unsubscribe containing mail currently use one-click URLs for unsubscribing since it's now required by Google and Yahoo. "mailto:" flow, while will be supported for a while, is pretty much obsolete at this point.
