We have been seeing examples of this all year, email providers increasing security on SMTP server processing, and forcing users to change how their email accounts are set up for tighter security. I did my own testing on gmail, confirming what you reported, that the FROM address to recipient will always be the SMTP-defined email address, not the from address.

I have no idea what references you used, because you did not include them.

However acm.org has a mail exchanged record in DNS that identifies the allowed mail server for email to come from as mail.mailroute.net See https://intodns.com/acm.org

So any mail server using reverse DNS or simple DNS to check the permitted origin of the email will reject it because the .ORG specifies where it's email comes from in DNS.

I can not go into the complexities of Googles mail offering and how it works with regard to sending from another address. It used to work, but Google, like Microsoft have for years resulting in their alias not working unless you send from the web site, tend to change the email headers to match what they have on their server for the account sending mail. If you have an issue with that, you will have to address it with Google. Thunderbird is a mail client and can send whatever it wants, but it can not control actions taken at the server based no corporate policies.

An email alias has allowed me to maintain the same external email address, no matter how many times my underlying email address has changed. If only a small percentage of email users used aliases the number would still probably run in the millions. The concern to prevent spoofing is a serious one. For several months I have been getting almost daily email rejection messages for messages I never sent. Yet the move to protect emailers from spoofing has run roughshod over the uses of aliases, which many of us find to be of great value. My alias email address is my user ID or registered email address in scores of websites and phone apps. It would be quite a nightmare to change them. Surely, major email providers, like Gmail, could allow you not just to register an alternative address, but to use it to send messages.

Matt, My general appeal above was written before I saw your response. I have difficulty following "However acm.org has a mail exchanged record in DNS that identifies the allowed mail server for email to come from as mail.mailroute.net See https://intodns.com/acm.org." In English, does this mean that ACM provides a means of specifying the outgoing server, but there are problems with it? I followed the link you provided and found:

   Your MX records that were reported by your nameservers are:
   10   mail.mailroute.net   199.89.1.120 199.89.3.120 (no glue)
   [These are all the MX records that I found. If there are some non common MX records at your nameservers
    you should see them below. ] 

I don't what this means. I have tried adding my acm.org address as a sending address to Google, but keep getting error messages, even though Google has verified several times that I can receive messages at that address. As you say, I need to take that up with Google. The basic question is: Do you know of an outgoing email server that allows you to send messages from an alias that you can register with it and the server can then verify to any recipient server that the message came from you?

What it means is the domain is set up to tell the world that the only acceptable server that mail from the domain can originate is mail.mailroute.net

Only effecting change or sending from that domain is going to see mail accepted with the big players.

Wikipedia offers a fairly introductory explanation of MX https://en.wikipedia.org/wiki/MX_record

You should also be aware that most of the big players also use DKIM, SPF and DMARC or some combination of them to validate a sender and sending domain. They have been around for a long time and are often used by SPAM filters. But a general overview is here https://www.csoonline.com/article/564563/mastering-email-security-with-dmarc-spf-and-dkim.html

Fundamentally I think you need to talk to the folk at ACM.ORG as they state that a membership benefit is an email forwarding address. https://myacm.acm.org/dashboard.cfm?svc=eforward

If i may jump in here with an opinion: Alias addresses (as documented in such places as here: https://en.wikipedia.org/wiki/Email_alias ) were never intended to be used in sending messages. In this case the ACM alias is useful to use when subscribing to mailing lists and organizations without need to change when the read address changes. Where it goes wrong is when the alias is used to send. The encroaching tightening of security is closing the coffin on that technique.