Outgoing email stopped working

Bellsouth.net is an att (legacy) account and as such you should be using the att specified server settings defined here.  Also read the part about using a secure mail key there.  You may also need to change your email password for your account and mentioned in the announcement at the top of this page.  Verify you can log into the webmail using the account password too.

Note, whatever you set your client's reply-to setting has no affect on send or receive by that client.  That's only for the recipient when they attempt to reply to an email you sent.  It doesn't even have to be valid!  Spammers spoof the return address all the time!   In Thunderbird the reply-to is set in the account's Default Identity - the panel you see when you click the account name in the left panel where the mailboxes are listed.

This did not provide a soln. I generated a secure mail key and added that as my password in both the incoming POP and outgoing SMTP servers. I continue to be able to access/download email using the secure mail key (as I was via the account password as well) but I cannot send email via the ATT SMTP server.

The problem is definitely due to the reply-as address. If I use the bellsouth.net email address as the reply address, I can send. If I use the reply-to email address Ive been using professionally for 20+ years (and 15+ years as a Bellsouth/ATT customer), I cannot send (the outgoing SMTP settings use the correct bellsouth.net account details).

I spent > 60m on technical support this afternoon and they report that Yahoo changed a bunch of things that caused email to not work for many people at the moment (presumably that's why I was kicked out of email altogether until I signed in to Yahoo).

I don't know what to tell you.  I also use TB and have TB's Default Identity (reply-to info) set to another (albeit non-att) email address.  It has always worked.   But then I don't have a legacy account.

Update:

As an experiment I  changed my identity info in TB for my account to an invalid email address.  And sure enough I got an error message when I tried to send.  So the server (att/yahoo's at least) does validate the reply-to email address!  Based on this I would say that whatever address you are setting the reply-to to is the source of the problem as you discovered.  You need to figure out what's going on with that other account not the account that's using it as the reply-to setting.

Just got done troubleshooting this identical issue (except my address isn't bellsouth). i was given a number that wasn't this connectech pay me thing. l'll post if anything comes of it. interesting your issue started about the same time as mine. Something changed somewhere. Mine started working about 2 days ago for 1 day on all platforms, pc/laptop/mobile device then stopped again. had me thinking it had been fixed but nope.

This problem came up a few days ago - nothing changed on our end - I'm using the same browser as I've always used.

Browser = Seamonkey - the updated old Netscape - it's Mozilla - Firefox based similar to Thunderbird.

Problem: In sending emails there is a 'Reply-to' button - up until now everything has worked fine.

Now I'm getting this error message - "An error occurred while sending mail. The mail server responded:  Request failed; Mailbox unavailable. Please check the message and try again."

The error message only occurs when there is a non - @att.net email address in the 'Reply-to" button space. When I put an @att.net email address in the "Reply-to" line - the email goes through with no error message. I've tried it using different domain email addresses ... @gmail.com and @live.com, etc..

Also - your phone lines are hacked - I called att customer service and a vacation sales pitch answered.

@atxatx1 

There have been a number or reports in the last 2 days about the "Mailbox unavailable" error occurring when the reply-to email address is different (or maybe just not an att/yahoo) from the account email address.  Other than mentioning that I don't know why this is suddenly happening since I cannot reproduce it (yet) and I use a non-att reply-to.  But mine is also set in the webmail reply-to account settings too.  The difference is that the webmail setting was done many years ago so I don't know if it would work today if I tried to change it.  Not going to test that either!   This may be a (crude) attempt by yahoo to discourage spammers using the yahoo servers who spoof the reply-to. 

Update:

Is your reply-to also set in your send-only address(es)?  Apparently to create those it goes through a verification process where it sends an email to the send-only address that that email needs to respond to (has a "click here" in the message).  Maybe that's the problem.

@atxatx1 

We have a business email address in the reply-to line that we can't use because of this problem.

Let me repeat my question again at what I am trying to find out.  Since Seamonkey is both an email client (more or less like Mozilla Thunderbird - I use that) and a browser (more or less like Mozialla Firefox), are you using the att/yahoo webmail interface accessed through start.att.net to send email or the email portion of Seamonkey? Whichever you are using for sending I am asking what the att/yahoo webmail settings are for send-only addresses and the account's reply-to.  I am defining "webmail" here as the att/yahoo email you access through start.att.net.  I am using the word "client" or "email client" when referring to Seamonkey's own email interface.

To access the webmail setting s go to start.att.net and click the settings gear -> more settings -> mailboxes.  Is the reply-to email address you want to use listed as a Send-only email address?  And if so it doesn't have a red triangle next to it "not verified"?  That would mean you can't use that address in a reply-to field.

If you are using Seamonkey's email as your client then in its mail settings the email address in the Default Identity should be whatever you have set for the reply-to in the webmail reply-to settings (maybe, see below).    It should also be a verified email send-only address shown in the webmail.  That identity's email address is what supplies the reply-to when you compose in the client.

I am no sure if there is a 100% tie in between the identity email address the client supplies its reply-to when you compose there and the current reply-to in the webmail's reply-to setting.  But I suspect there is a check of the reply-to you set in the identity and the list of webmail send-only addresses.  I assume if they are not verified (which is done when you create them) or not even in the list then the server isn't even going to let an email client use it either.  I didn't test this out.

In the webmail's same mailboxes pane click your email account.  The pane on the right will show, among other things its Reply-to setting.  It's either going to show your account or one of the send-only addresses (if any) and if it is one of the send only addresses it should be one that is being flagged as not-verified.

So it's the webmail's send-only and reply-to settings I am asking about and how it correlates with the client's Default Identity email address setting.  And if you are not using Seamonkey's email just the webmail's settings.

As follow up to your note, I wanted to say that I just gave up on AT&T. I do not know if there is a new way to verify these email addresses on the new Yahoo (there was on the old Yahoo) but no one at AT&T could tell me how to do it. I have just switched over to using  a Google account -- Google understands the need for a send/reply-to address that is different from the ISP email address and makes it painless to set up. I set it up, verified, and had it set up in Thunderbird (as well as the gmail app) all in about 10m. I think the "galactic size company" is the main issue here.  When I went to my professional association website, it said I had set up the mail forwarding to the bellsouth account in 2003. So it worked for 15+ yrs but no one at AT&T thinks it should have ever worked that I was able to talk to.

I have just switched over to using a Google account

Ever since there has been this cluster of these "reply-to different from account" problem reports I thought to myself "if they always have used a personal reply-to not just move to a real email service provider (ESP) that actually knows how to run an email service?".  In other words, what you did.  That's probably the one of the main reasons for using a personal domain or forwarding service, i.e., to allow you to trivially move to any ESP and your contacts never know nor care.  To them your email address never changes.

I use the same forwarding service since the 90's.  While my reply-to works with my att email I could care less if it goes belly up.  No one has ever used my att email since I never use it except for testing purposes.  Also I too use a different ESP (not gmai).