Not having your modified Client3 code, I substituted Net::SMTP::Server::Client2, and your code seems to work just fine. Here is a clip of the telnet session: 

220 Debatable SMTP 0.2 Ready.
HELO

250 OK Welcome
HELO

250 OK Welcome
DATA

503 start with 'mail from: ...'
HELP

214-Commands

214-DATA EXPN HELO HELP MAIL
214 NOOP QUIT RCPT RSET VRFY
NOOP

250 Whatever.
RSET

250 buffahs ah cleah, suh!
VRFY

252 Nice try.
EXPN

252 Nice try.
MAIL

501 could not find name@postoffice in <>
RCPT

553 no user@host addresses found in <>
QUIT

221 Ciao

[download]

And the associated console trace: 

C:\test>647478
Launched Thread Number 1
Use of uninitialized value in numeric eq (==) at C:\test\647478.pl lin
+e 58.
Client Processing Started
GOT IN HERE
1172 command: HELO
1172 command: HELO
1172 command: DATA
1172 command: HELP
1172 command: NOOP
1172 command: RSET
1172 command: VRFY
1172 command: EXPN
1172 command: MAIL
1172 command: RCPT
1172 command: QUIT
Client Processing Finished

[download]

So, apart from not having any mail or users to retrieve, everything seems to work as designed. It suggests that your modifications to produce Client3 are probably at fault. My best suggestion is that you return to Client2 and then add back your modifications step by step to see what causes the breakage.

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.
"Too many [] have been sedated by an oppressive environment of political correctness and risk aversion."

In reply to Re: Using Threads For Simple SMTP Relay Server by BrowserUk
in thread Using Threads For Simple SMTP Relay Server by lamberms

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