proton mail: "Note that you can’t compose new messages from scratch using +aliases, but you can reply using the +alias to messages sent to that address."

That's some missing functionality

Also don't see anything about a token other than +

https://proton.me/support/addresses-and-aliases

#SubAddressing

Types of email addresses and aliases | Proton

Learn more about Proton Mail addresses, including free personal addresses, aliases, and custom addresses with your own domain.

Proton

KnownHost lets you set your own delimiters for #SubAddressing , which is awesome

https://www.knownhost.com/kb/how-to-configure-subaddressing-plusaddressing-in-directadmin/

But, it's making config changes in a VPS. In this case I'm setting up for someone else who I don't want to depend on me for tech support

Seems to be common setup for #KnownHost so that might be sufficient, but I'd really prefer a mail hosting solution rather than VPS in this case

+ gets blocked by too many sites, so I'd have to provide too much tech support to go with plus or a catch-all

How to Configure Subaddressing/PlusAddressing in DirectAdmin? - KnownHost

Subaddressing is known as plus-addressing or detailed addressing & describes the ability to send email to an address contains email username

KnownHost

ICDSOFT uses dash for #SubAddressing

Never heard of ICDSOFT, but they just became my favorite mail hosting company :)

https://www.icdsoft.com/en/kb/view/2139_email_subaddressing

#MailHosting

Online manual | ICDSoft

Quality Web Hosting since 2001. Free Site Migrations, 99.9% uptime, 24/7 tech support, 15-minute response guarantee. Three datacenter locations. Up to 90% discount for resellers.

ICDSoft Ltd.

Looking at FastMail for someone and it looks like they only allow plus for subaddressing

WikiPedia indicates this is a common problem

https://en.wikipedia.org/wiki/Email_address#Sub-addressing

Any suggestions for good mail hosts that allow you to bring your own domain and allow another #subaddressing token?

I'd like to use dot, but dash could work as neither is generally blocked by poorly configured websites like plus

Subdomain is cool, but not what I'm wanting to explain to the recipient of this shiny new mail setup :)

Email address - Wikipedia

Was writing a mail to my ISP; A few months back I changed my mailadres using + #subaddressing, but that broke the internal system as the logon name didn't support + addressing but did accept it for mail.
Now there was a mismatch [email protected] != [email protected], couldn't check my invoices etc…
Wanted get that fixed, wrote a whole mail explaining #RFC5233. But before sending decided to check it again. And now they do accept + in logon! Should've checked before typing this long mail πŸ€“

I hate booking forms (and others, but specifically bookings) that don't accept subaddressing (plus-addressing) in email addresses and insist on "you must enter a valid email address". You stupid brain dead web developers! Read and understand that damn RFC 5233!
https://www.rfc-editor.org/rfc/rfc5233

Or if that's too sophisticated for you then at least Wikipedia
https://en.wikipedia.org/wiki/Email_address#Subaddressing

#SubAddressing #PlusAddressing #Email #Forms #stupid #brainDead #Web #Developers #RFC5233

RFC 5233: Sieve Email Filtering: Subaddress Extension