> 1. I changed my virus settings so that outoing e-mail is not scanned
> (although I'd like to put that back on once I'm sure everything is
> back to normal).
I'd recommend against turning this back on since this is not normally necessary and if it is you have a whole lot more problems on your system than sending a virus. In any case this sort of scanning causes more problems than it solves.
>
> 2. I reinserted passwords under my various accounts, just in case
> they had gotten scrambled.
I assume you are talking about SMTP authentication since any receiving will not be causing your mail not to be sent. In addition, if you have a failure of authentication then it will be seen as you send.
>
> 3. In trying to solve an earlier problem (where the wrong return
> e-mail was being inserted), in flailing around for a fix, under
> Internet Mail Options, Sending, I clicked on "Use and alternate
> e-mail address for the SMTP envelope) and inserted my e-mail
> address there. I unchecked that.
This also should not have caused any problem that you would not see immediately upon sending.
>
> Whatever it was, I've spent the morning doing follow-up e-mails to
> everyone I tried to contact over the past week and am just relieved it
> all seems to be working.
If mail is being accepted by your ISP without error and is not received by a different host I suspect your are being caught in some sort of spam trap where the mail is quietly deleted when caught rather than being bounced back at the SMTP host. This is typical since most spam traps that catch the mail after receipt by the SMTP host, they almost never bounce the mail back to the receiver since the addresses in the mail body are generally faked.
> 1.  I changed my virus settings so that outoing e-mail is not scanned
>     (although I'd like to put that back on once I'm sure everything is
>     back to normal).
I'd recommend against turning this back on since this is not normally necessary and if it is you have a whole lot more problems on your system than sending a virus.  In any case this sort of scanning causes more problems than it solves.
>
> 2.  I reinserted passwords under my various accounts, just in case
>     they had gotten scrambled.
I assume you are talking about SMTP authentication since any receiving will not be causing your mail not to be sent.  In addition, if you have a failure of authentication then it will be seen as you send.
>
> 3.  In trying to solve an earlier problem (where the wrong return
>     e-mail was being inserted), in flailing around for a fix, under
>     Internet Mail Options, Sending, I clicked on "Use and alternate
>     e-mail address for the SMTP envelope) and inserted my e-mail
>     address there.  I unchecked that.
This also should not have caused any problem that you would not see immediately upon sending.
>
> Whatever it was, I've spent the morning doing follow-up e-mails to
> everyone I tried to contact over the past week and am just relieved it
> all seems to be working.
If mail is being accepted by your ISP without error and is not received by a different host I suspect your are being caught in some sort of spam trap where the mail is quietly deleted when caught rather than being bounced back at the SMTP host.  This is typical since most spam traps that catch the mail after receipt by the SMTP host, they almost never bounce the mail back to the receiver since the addresses in the mail body are generally faked.
