Subdomain addressing does not work for me
 

I have a domain, mydomain.tld managed by Fastmail DNS
I've set several aliases for family members that redirect to their email provider (for example, wifesname@mydomain.tld forwards to wife's gmail) and a wildcard *@mydomain.tld that forwards to mine.

I would expect anything@wifesname.mydomain.tld to land in wife's inbox (on gmail), but instead it lands in mine.

What gives?

Odd. Does "wifesname" contain anything other than alphabetic characters?

Nope, purely alphabetical.

How are you doing that forwarding? Are you using the alias's Deliver to target setting? Not sure how you create a FM alias using your own private domain since I don't have any of those.

Using FM's aliases I do know that if I create an alias testit@mm.st with a target (Deliver to) specified as mygmailacct@gmail.com and send an email to xx@testit.mm.st, the gmail account will receive the email message with it's To set to xx@testit.mm.st. and its Deliver To header mygmailacct+xx@gmail.com (which is how gMail handles these kind of subdomain addresses).

In your cases that fail what does the message's Delivered-To say?

The more I think about this, the stranger it seems. This is a feature that has existed in Fastmail almost from the beginning, and is heavily used. The way it is implemented is independent of things like the sieve script (which could be faulty in some way). The only thing I can think of is that the configuration for your domain has not been correctly transmitted to one or more of Fastmail's MX servers. Maybe, you should raise a support ticket, and have the support staff investigate that possibility.

EDIT: You could try deleting the alias for your wife, saving the configuration, waiting a few minutes, and then adding it back. Maybe, if there was a hiccup with the MX server updates, this would resolve it. Even then, it might be important to report it.

Subdomain routing setting
 

In the edit screen for your domain at Fastmail, the last item shown is Routing. You can manage the routing with several choices:

• Subdomain routing: If you set this incorrectly you won't get delivery to the proper user based on the subdomain. You normally want to have this set to the first choice.
• Routing: This should be set to internal if your email is delivered to the normal Fastmail servers.

You can also see Fastmail Help concerning these settings.


Bill

Thanks Bill, it was the routing setting. It was set to the 2nd option.
https://www.fastmail.com/settings/domains/25463/routing

Glad that fixed it! With choices comes the possibility of incorrect settings of those choices. I believe that the main reasons that Fastmail removed some of their previous flexibility over the past few years was to reduce user error and simplify support.

Bill