Is it worth trying the generic TCP/IP reset?
netsh int ip reset (from https://support.microsoft.com/en-us/kb/299357 )

We are currently experiencing mail delivery failures, but not consistently.  The deliveries return the following error message to the user:

Delivery has failed on the enclosed message for the following reasons reported either by the mail delivery system on the mail

relay host or by the local TCP/IP transport module:

*** TCP/IP error while processing job ***

In most cases, I find the emails have eventually been sent from their queue, but I am not sure what is causing this problem.  I have checked with our email host and they claim to have not made any changes that would cause this. Can anyone advise of tools or tests I can use to see if the problem is related to the traffic on my LAN?  This situation just started in the last few weeks and is not consistent.  We only run Pegasus and each PC runs it from their harddrive, but folders are on a network share.  We send all email via internet using POP3 and SMTP.  Any advice appreciated.

I would suspect a TCP/IP timeout right off the bat. I'd try increasing the timeout setting.

Before we started using Mercury32, we had a similar setup. We used a single account to send company email, where all staff mail accounts would forward mail to be sent to the single account. When I had to check the account I often saw this message.

I never discovered why this message appeared. I suspect the network was simply busy. However, even though I saw these messages, I never had failed sent mail, unless the Internet connection failed.

I simply ignored the message unless it was repeated.

I have been increasing SMTP setting as problems are reported...usually doubling whatever I find there.  The lowest I've seen is 15 seconds and the most is 60.  It still happened when one user already had 60 seconds...is there any rule of thumb of what should be adequate?  Should I also increase the POP3 setting?  It only seems to be a problem with sending (although users have options checked to do both each time) so I haven't been changing the POP3 setting.

I always set mine to 180 seconds.  Rarely do I have to set it higher.

[quote user="Catherine"]I have been increasing SMTP setting as problems are reported...usually doubling whatever I find there.  The lowest I've seen is 15 seconds and the most is 60.  It still happened when one user already had 60 seconds...is there any rule of thumb of what should be adequate?  Should I also increase the POP3 setting?  It only seems to be a problem with sending (although users have options checked to do both each time) so I haven't been changing the POP3 setting.[/quote]

I set mine to 180 as a minimum and Mercury/32 runs at 300 seconds minimum.  Remember this is a timeout setting and it the time that the client/server will wait until the other host responds during a transfer.  It has nothing to do with how long the connection normally remains in place.

Thanks...I will increase settings as suggested. For my own understanding....Does increasing the timeout to a level higher than the POP3 polling control frequency have any negative implications?  ie...with timeout at 180 and POP3 polling at 60, there could be separate sending and receiving transfers happening at the same time, right? 

[quote user="Catherine"]Thanks...I will increase settings as suggested. For my own understanding....Does increasing the timeout to a level higher than the POP3 polling control frequency have any negative implications?  ie...with timeout at 180 and POP3 polling at 60, there could be separate sending and receiving transfers happening at the same time, right? [/quote]

Doubt it.  If the POP3 session is active downloading a really large amount of mail the POP3 would not be polled since it was already active.  The timeout  setting just controls how long the system will wait duing an active session so it should not work any different than getting a lot of mail.  That said, I've set the POP3 poll interval a lot shorter than the timeout settings with no problems at all in both MercuryD and WinPMail.

Have only ever used Pegasus, I have been using webmail through my

> > provider.

>

> > This first started out with a 550 authentication error, I contacted my

> > ISP and changed a port setting. Now depending on which place I check

> > in SMTP>Security>SMTP Authentication I get either a *** TCP/IP error

> > while processing job *** or a 550 Please configure your mail client to

> > use authentication.  

[quote user="david17"]

Have only ever used Pegasus, I have been using webmail through my > > provider. > > > This first started out with a 550 authentication error, I contacted my > > ISP and changed a port setting. Now depending on which place I check > > in SMTP>Security>SMTP Authentication I get either a *** TCP/IP error > > while processing job *** or a 550 Please configure your mail client to > > use authentication.  

[/quote]

Please supply more details of what error you get when.  Also, what are your SSL settings?