I do this too. It's worth noting that you don't need to host your own email server to do this. I personally use Migadu as an email host for my own domains which lets me define arbitrary wildcard redirects. I'm sure most of its competitors will let you do the same.
Note that Gmail also supports dots as well (similar to your postfix solution).
Not quite, it's not a separator, you can't add arbitrary content after the dot. Dots are just ignored in Gmail, so you need to keep a map of dot placement and quantity to service, vastly less convenient.
Yes, you're right. The dots thing isn't as powerful as the + separator. But it is useful for sites that have a poor understanding (or regex) associated to their address validator. In context of the parent comment, that's the point, that the dots aren't restricted as the plus separator can be.
Do you ever have issues sending messages using user.acme@example.com as the from address?
Some companies want you to respond from the email address on file when you interact with them.
I do something similar except I make up a custom email every time. (No plus addressing at all, everything without a valid destination goes to the default account) It's rare something doesn't like it, most automated systems use the reply to header. Email lists are usually the ones least tolerant.
No, most companies that get the special email treatment don't accept email from customers anyway.
If I did it, I would have to set it manually. I don't know of an email client that supports setting the From header to the address in the To header of the relied-to message, but it feels like something that would be fairly easy to do as a Thunderbird plugin or whatever.
Gmail has supported this for a long time with the '+' character, but this has some major problems. Many things that accept email addresses don't recognize '+' as a valid email username character and won't let you submit the form. I hypothesize that some of this is poor awareness of what constitutes a valid email address, and some of it is intentional to force users to input their "real" email address. I have also run across a few systems that stripped off the '+' suffix off my gmail address.
My solution is to use the '.' as the separator because 'firstname.lastname' is a VERY common email username and I'm happy to not allow it in a "real" username on my tiny mail host.
So every new site or company I interact with gets user.acme@example.com instead of my "real" email address. I can filter incoming emails based on the To header. And I even have a list of companies (a couple well-known) that have leaked or sold my email address to spammers. Some day I'll write a blog post about that.