[truemagic]

Originally Posted by n5bb

This works correctly if you pay attention to the details. If your account is username@fastmail.com:

• Emails sent to "foldername@username.fastmail.com" will be automatically delivered to your folder "foldername" (if it exists).
• If the "foldername" folder does not exist, the email will be delivered to your Inbox.
• Emails sent to "foldername.subfoldername@username.fastmail.com" will be automatically delivered to your subfolder "foldername.subfoldername" (if it exists).
• Of course, if your account is at a different Fastmail domain (such as sent.com), you need to replace "fastmail.com" with the other domain name (such as "sent.com").
• Read more at Fastmail Help.

There are a few more details involved when using your own custom domain "mydomain" hosted by Fastmail:

• In Settings>Domains, click Edit and examine the setting for Routing. The default is "Accept mail to anything@user.mydomain and deliver it to user+anything@mydomain.". This performs the same trick to move the subdomain address to the initial part of the delivery address so it defines the top-level delivery folder.
• In Settings>Team & Sharing>Team addresses you set up the email addresses you want to use for incoming messages, both at Fastmail domains and your private domain, and how to deliver messages sent to those domains. You can set up specific aliases at your domain, such as "bob@mydomain" and "alice@mydomain", and you can also set up a catch-all (wildcard) if an incoming message is sent to "bobb@mydomain" (which you didn't set up a specific alias to handle). See Fastmail Help for instructions on how to set up the catch-all. Since you can specify the Deliver to details for the catch-all wildcard, you can create a folder to hold those rogue messages (such as "wildcard") and deliver the messages which don't match an alias to the wildcard folder by specifying a Deliver to address of "username+wildcard@fastmail.com" or whatever Fastmail domain your account is using.
• If you set up the alias "bob@mydomain" to deliver to the "bobby" folder, incoming messages to "bob.games@mydomain" will be delivered to the "games" subfolder of the "bobby" main folder (if those folders and subfolders exist). If the subfolder does not exist, the message is delivered to the "bobby" folder, and if that folder does not exist to your Inbox. The alias delivery directions override the default folder and subfolder delivery methods.

All of this works very well. I have been using this system for many years. Recently (a few month ago, I believe) Fastmail added the ability to specify the Deliver to for the catch-all wildcard custom domain, and it's very useful to discover when spammers are trying random usernames at your domain name.

Bill

Thanks Bill, for the comprehensive explanation. I'm still trying to get some of these to work, and I appreciate the help very much!