e-mail validity checkers?

DougLass · 16 Apr 2024, 01:48 AM

So I get hard bounces from a couple of e-mail addresses. I run these addresses through several commercial free e-mail testers, and I get back that they are valid. In fact, I KNOW they are not valid. These folks have just left the company or retired. Do these testers use some list that is not frequently updated?

n5bb · 16 Apr 2024, 01:55 PM

There are a range of different techniques used to check that an email is likely to be delivered. Some just look at the format of the message you are sending, including SPF, DKIM, DMARC, etc. These techniques don't actually check the target delivery address.

Tools can also check the delivery domain, DNS records, and delivery MX server. These insure that there is actually a server which can be reached which accepts email for that domain.

A more extensive test can start a SMTP session with the delivery MX server using the target email address, then stop this process before an actual email is transferred. This can check that the recipient address is actually accepted at the destination.

But the destination system can choose to reject the email later during the SMTP connection stage (due to the sending server used, the source email address, the destination email address, or other criteria designed to delay acceptance of the message, since spam sending servers often give up if the initial connection is rejected).

In some cases the message might be initially accepted, then a non-delivery message is sent back to the sender. You can't fully test in that case until you actually complete sending of a full message which isn't blocked by a spam filter. I think that the testers you have tried only check the low-hanging fruit.

Bill

DougLass · 17 Apr 2024, 01:36 AM

Thank you. Can you point me to a service that actually tries to connect with the destination server? If that destination server rejects it, so be it. But at least I know what's going on. Services that just check my own e-mail, to make sure it is compliant, are NOT checking someone else's e-mail.

16 Apr 2024, 01:48 AM	#1
DougLass Member Join Date: May 2014 Posts: 56	e-mail validity checkers? So I get hard bounces from a couple of e-mail addresses. I run these addresses through several commercial free e-mail testers, and I get back that they are valid. In fact, I KNOW they are not valid. These folks have just left the company or retired. Do these testers use some list that is not frequently updated?

16 Apr 2024, 01:55 PM	#2
n5bb Intergalactic Postmaster Join Date: May 2004 Location: Irving, Texas Posts: 8,928	There are a range of different techniques used to check that an email is likely to be delivered. Some just look at the format of the message you are sending, including SPF, DKIM, DMARC, etc. These techniques don't actually check the target delivery address. Tools can also check the delivery domain, DNS records, and delivery MX server. These insure that there is actually a server which can be reached which accepts email for that domain. A more extensive test can start a SMTP session with the delivery MX server using the target email address, then stop this process before an actual email is transferred. This can check that the recipient address is actually accepted at the destination. But the destination system can choose to reject the email later during the SMTP connection stage (due to the sending server used, the source email address, the destination email address, or other criteria designed to delay acceptance of the message, since spam sending servers often give up if the initial connection is rejected). In some cases the message might be initially accepted, then a non-delivery message is sent back to the sender. You can't fully test in that case until you actually complete sending of a full message which isn't blocked by a spam filter. I think that the testers you have tried only check the low-hanging fruit. Bill

17 Apr 2024, 01:36 AM	#3
DougLass Member Join Date: May 2014 Posts: 56	Thank you. Can you point me to a service that actually tries to connect with the destination server? If that destination server rejects it, so be it. But at least I know what's going on. Services that just check my own e-mail, to make sure it is compliant, are NOT checking someone else's e-mail.