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n5bb · 11 Jan 2021, 01:50 PM

Welcome to EMD and also to Fastmail!

I have had a Fastmail account hosting my own personal domain since 2004 (17 years), the same year I joined the EMD forum. Fastmail has grown into a very solid company with a great service in that interval.

I never use my login address for my main Fastmail account for email. Instead I use aliases and subdomain addresses at those aliases, both at Fastmail domains and my own personal domain. In the examples below, let's assume that your Fastmail login address was jcitizen@fastmail.com. I'm sorry that my post is so long and complex, but I wanted to give you an idea of how you can use subdomain addressing so you don't need to create a new alias for every company you interact with.

You can create email aliases at many Fastmail domains. For example, you could use example@sent.com, where "sent.com" is one of the Fastmail-owned domains you can use. You can also create aliases at the domain(s) you own which are hosted at Fastmail.
It's much easier when signing up at businesses or organizations who will send you messages to use subdomain addressing. If you control the alias "example@sent.com", then you can use any number of subdomain addresses such as "alpha@example.sent.com" or "beta@example.sent.com" without explicitly creating an alias for that complete address. You just create the alias "example@sent.com" and anything@example.sent.com is a valid address which will be delivered to your account. The alias name becomes the subdomain after the @, and is separated from the main domain name by a period/full-stop symbol (.).
During delivery at Fastmail, the subdomain address is by default expanded to a plus address before delivery is made. So "alpha@example.sent.com" is changed to "example+alpha@sent.com", which by default causes the message to target your "alpha" folder if it exists, and your Inbox folder if that specific folder does not exist, assuming that the alias table target is your Inbox. You will see in the full headers that the X-Delivered-To header is "alpha@example.sent.com" and the X-Resolved-To header is "jcitizen+alpha@fastmail.com", which causes the message to by default be filed into your "alpha" folder (if it exists).
But you can change this behavior by changing the alias target (in the alias setup page). If the "example" alias target is changed to "jcitizen+*@fastmail.com", the wildcard * causes the X-Resolved-To header to become "jcitizen+example.alpha@fastmail.com", which leads to the message being filed into the "alpha" subfolder of the top-level "example" folder. The full-stop period "." character denotes a subfolder. You can also add more than one alias target so that messages sent to that address are delivered to more than one folder. The alias resolution happens before spam processing.
So let's say that you have accounts at various financial institutions and you want messages from those companies to always be filed into the "bank" folder (and possibly subfolders of bank for specific companies). You could create the alias "bank" at your personal domain, and use as the target for that alias "jcitizen+*@fastmail.com" on the alias setup page. Here is how messages would be filed from various companies:
- Messages sent to "bank@yourdomain.com" would be filed into the "bank" folder.
- Messages sent to "alpha@bank.yourdomain.com" would be filed into the "alpha" subfolder of the "bank" folder if that subfolder exists. Otherwise they would be filed into the "bank" folder if the subfolder does not exist.
- You could set up several companies in this fashion. You don't have to create a new alias for each one -- only the one alias "bank" is needed. If the proper subfolder does not exist, the message will be filed in the main "bank" folder.
- Capitalization is ignored in email addresses and folder names during automatic email delivery processing.
See the Fastmail help page about subdomain addressing at: https://www.fastmail.com/help/receive/addressing.html
When I say that the emails will be automatically filed into the folder as described, this really means that at the first processing stage (before your rules are executed, the X-Resolved-To header is used to target a specific delivery folder rather than the default Inbox. The rules are then executed, and rules can over-ride the target folder described above.
Even if you don't want to create a specific subfolder for each company, using subdomain addressing still makes things much easier for you. The subdomain (alias) name can be something which would be unlikely to be guessed by a spammer, and you can add the company name before the @ when you sign up (anything@bank.yourdomain.com) and won't need to create a new alias. You just create one alias for the subdomain (such as "bank" in my example).
If there is a security breach, you can discover this because you only gave that specific subdomain address (alpha@bank.yourdomain.com) to that one company. If the address is used by anyone else, it means that the company has sold their address list to another company or a spammer/scammer has stolen it.

Bill

11 Jan 2021, 01:50 PM	#3
n5bb Intergalactic Postmaster Join Date: May 2004 Location: Irving, Texas Posts: 8,929	Using subdomain addressing to simplify the use of many unique addresses Welcome to EMD and also to Fastmail! I have had a Fastmail account hosting my own personal domain since 2004 (17 years), the same year I joined the EMD forum. Fastmail has grown into a very solid company with a great service in that interval. I never use my login address for my main Fastmail account for email. Instead I use aliases and subdomain addresses at those aliases, both at Fastmail domains and my own personal domain. In the examples below, let's assume that your Fastmail login address was jcitizen@fastmail.com. I'm sorry that my post is so long and complex, but I wanted to give you an idea of how you can use subdomain addressing so you don't need to create a new alias for every company you interact with. You can create email aliases at many Fastmail domains. For example, you could use example@sent.com, where "sent.com" is one of the Fastmail-owned domains you can use. You can also create aliases at the domain(s) you own which are hosted at Fastmail. It's much easier when signing up at businesses or organizations who will send you messages to use subdomain addressing. If you control the alias "example@sent.com", then you can use any number of subdomain addresses such as "alpha@example.sent.com" or "beta@example.sent.com" without explicitly creating an alias for that complete address. You just create the alias "example@sent.com" and anything@example.sent.com is a valid address which will be delivered to your account. The alias name becomes the subdomain after the @, and is separated from the main domain name by a period/full-stop symbol (.). During delivery at Fastmail, the subdomain address is by default expanded to a plus address before delivery is made. So "alpha@example.sent.com" is changed to "example+alpha@sent.com", which by default causes the message to target your "alpha" folder if it exists, and your Inbox folder if that specific folder does not exist, assuming that the alias table target is your Inbox. You will see in the full headers that the X-Delivered-To header is "alpha@example.sent.com" and the X-Resolved-To header is "jcitizen+alpha@fastmail.com", which causes the message to by default be filed into your "alpha" folder (if it exists). But you can change this behavior by changing the alias target (in the alias setup page). If the "example" alias target is changed to "jcitizen+@fastmail.com", the wildcard causes the X-Resolved-To header to become "jcitizen+example.alpha@fastmail.com", which leads to the message being filed into the "alpha" subfolder of the top-level "example" folder. The full-stop period "." character denotes a subfolder. You can also add more than one alias target so that messages sent to that address are delivered to more than one folder. The alias resolution happens before spam processing. So let's say that you have accounts at various financial institutions and you want messages from those companies to always be filed into the "bank" folder (and possibly subfolders of bank for specific companies). You could create the alias "bank" at your personal domain, and use as the target for that alias "jcitizen+@fastmail.com" on the alias setup page. Here is how messages would be filed from various companies: Messages sent to "bank@yourdomain.com" would be filed into the "bank" folder. Messages sent to "alpha@bank.yourdomain.com" would be filed into the "alpha" subfolder of the "bank" folder if that subfolder exists. Otherwise they would be filed into the "bank" folder if the subfolder does not exist. You could set up several companies in this fashion. You don't have to create a new alias for each one -- only the one alias "bank" is needed. If the proper subfolder does not exist, the message will be filed in the main "bank" folder. Capitalization is ignored in email addresses and folder names during automatic email delivery processing. See the Fastmail help page about subdomain addressing at: https://www.fastmail.com/help/receive/addressing.html When I say that the emails will be automatically filed into the folder as described, this really means that at the first processing stage (before your rules are executed, the X-Resolved-To* header is used to target a specific delivery folder rather than the default Inbox. The rules are then executed, and rules can over-ride the target folder described above. Even if you don't want to create a specific subfolder for each company, using subdomain addressing still makes things much easier for you. The subdomain (alias) name can be something which would be unlikely to be guessed by a spammer, and you can add the company name before the @ when you sign up (anything@bank.yourdomain.com) and won't need to create a new alias. You just create one alias for the subdomain (such as "bank" in my example). If there is a security breach, you can discover this because you only gave that specific subdomain address (alpha@bank.yourdomain.com) to that one company. If the address is used by anyone else, it means that the company has sold their address list to another company or a spammer/scammer has stolen it. Bill