Blocked emails: no way to identify undelivered invitations

I'd like to hear the answer to this. In organising a meeting taking place yesterday 15/9/21, of  73 who Registered, 15 said they had not received Confirmation emails, then not be able to join in.

Not a good %age.

There is inherently no way of any sending system to know for sure that a sent message has not been classified as spam along its route or by the recipients' systems or filtering.

Generally speaking it is a recipients responsibility to ensure their systems are not blocking the emails they are expecting. 

https://en.wikipedia.org/wiki/Bounce_message

"A bounce message or just "bounce" is an automated message from an email system, informing the sender of a previous message that the message has not been delivered (or some other delivery problem occurred). The original message is said to have "bounced".

https://support.cleverreach.de/hc/en-us/articles/202372821-What-Are-Bounces-and-How-Does-CleverReach-Handle-Them-

Here's an example how non delivered mails are handled in CleverReach and that they manage to provide an overview of undelivered mails.

I'd love to get some response from Zoom whether they plan to put some effort to provide a better experience here. We would really need to identify recipients who didn't receive the emails. 

Most of the time they don't register via Zoom but on a congress site, etc. and we just import the registrants.  Typos are not an issue for us but the many blocked mails, especially registrants with a meduniwien.ac.at domain comprising many of our customers.

Hi @philpav , @PoJo 

The challenge that exists here, is that not all mail servers will return a bounce message when an email is undelivered. Most will, in most cases, but not all.  This is particularly the case with spam filters.

It is therefore not guaranteed that a sender (or a sender's system) will always know if a sent message has been undeliverable to its final destination. 

Bad email addresses will almost always get bounced. But spam filters can often be configured to discard or quarantine email messages totally silently (without informing the sender).

Spam filters can be configured entirely at the discretion of the recipient's organization. Almost all end up with different rules and levels of sensitivity.

With quarantining, usually the recipient, or an intermediate system administrator, would be informed on, typically, a periodic basis - but this relies on them having a keen eye on their reports. The sender, however, or a sender's system, would usually have no way of knowing their message was quarantined (no bounce for quarantine).

If a spam filter has been configured to silently discard what it believes to be spam of a certain type, then there is simply no way to know. It may not be desirable, or pleasant, but it can happen.

Usually it is the responsibility of the recipient's organization to ensure they can receive email from their desired senders - patricianly when it comes to spam filtering.

If meduniwien.ac.at has a particular problem receiving email from Zoom, I would be leaning on them to fix that.