OK, this is strange.
When I send mail from one yahoo acct to another yahoo acct (as a test, I do not do this as a habit.)
I get an error. When I go to the outbox, I am able to send that same mail.
I have seen this in the past, but it was not repeatable.
This time it is repeatable.
Maybe this has been fixed in the next update?
I also have a problem with my MyWay account, probably just a temporary problem.
--- Version ---
OS: Windows 7 (x64)
POP Peeper: 4.3.0.9003
Webmail: 4.2.5.0
SSL: 1.0.1.8
IMAP: 4.3.0.0
RSS: 4.3.0.0
SendMail: 4.3.0.9003
Notification Voice: 4.3.0.0
Profile Picture: 4.3.0.0
AntiJunk: 4.3.0.0
Spell Checker: 4.3.0.0
Web of Trust: 4.3.0.0
--- Error ---
AAAYahooXXXXXXXXXXXX55IMAP [1000: IMAP] ['imap.mail.yahoo.com' (993) SSL: 1] [Smtp: 'smtp.mail.yahoo.com' (587) SSL: 2]
Send Mail: Login Error: Auth XOAUTH2
Server Returned: 4.3.2 Internal server error (#OCF014) (#451)
MywayXXXXX5555 [5: MyWay] ['' (0) SSL: 0] [WebSend: '' (0) SSL: 0]
Error: Try again later. (-10)
error when sending mail, but resend works
error when sending mail, but resend works
Last edited by mjs on Fri Nov 18, 2016 5:02 am, edited 1 time in total.
Reason: Edited to redact personal information for privacy/security concerns (re: posted email addresses)
Reason: Edited to redact personal information for privacy/security concerns (re: posted email addresses)
Re: error when sending mail, but resend works
It would appear you're having an OAuth2 log-in error problem sending mail. You could try exiting/restarting PP to see if this helps, but then since you're using a beta (test) build it would be better yet to just wait for Jeff to look into this issue later today. 
Good judgment comes from experience and a lot of that comes from bad judgment. - Will Rogers
Re: error when sending mail, but resend works
POP Peeper cannot do anything about an "internal server error" as that is expressly an issue with Yahoo's servers. I did a search for that specific error code and it doesn't seem very common, but there was a reference to it (for Yahoo mail) from a couple years ago. Hopefully it's just a temporary issue and you'll be back to normal again soon.