POP retrieval not working anymore

Problem reported by Tom - 3/16/2025 at 2:36 PM

Submitted

Using SM Free Edition v16.3.6989 on Windows server 2008 R2 (WHS 2011).
Since 3 days the (automatic) POP retrieval is not working anymore for 4 user accounts.
Nothing else has changed.
The (detailed) POP Retrieval Log shows
[2025.03.16] 21:54:57 [user@domain] [pop.isp.be:userid@isp.be] Connection to xxx.xx.x.xx succeeded
[2025.03.16] 21:54:57 [user@domain] [pop.isp.be:userid@isp.be] Could not understand servers response to connection
[2025.03.16] 21:54:57 Finished processing for user@domain
Testing the connection in Settings - Connectivity - Email Retrieval always says "Connection test failed"
No change after restarting SM service or the complete server.
I deleted the retrieval for one user and created it again but don't succeed to save it because the failing test.
Testing via openssl is working fine, connection is ok and retrieving email is possible !
openssl s_client -crlf -connect pop.isp.be:995 -brief
CONNECTION ESTABLISHED
Protocol version: TLSv1.3
Ciphersuite: TLS_AES_256_GCM_SHA384
Peer certificate: C = BE, ST = Brussels Hoofdstedelijk Gewest, L = Schaarbeek, O = Proximus NV, CN = pop.isp.be
Hash used: SHA256
Signature type: RSA-PSS
Verification: OK
Server Temp Key: ECDH, prime256v1, 256 bits
+OK InterMail POP3 server ready.
user userid@isp.be
+OK please send PASS command
pass **********
+OK userid@isp.be is welcome here
stat
+OK 16 2565548
...
I've been looking around (almost) everywhere, but did not find any clue to resolve this.
Anybody to point me in the right direction ?

6 Replies

Reply to Thread

Kyle Kerst Replied

3/17/2025 at 7:52 AM

Employee Post

Does the UserID contain characters that might require UTF8 support by chance?

Kyle Kerst

Lead Internal Network/System Administrator

SmarterTools Inc.

smartertools.com

Tom Replied

3/17/2025 at 12:21 PM

Hi Kyle,
No, the userid only contains a..z and 0..9.

And the pop retrieval has been working for years.

J. LaDow Replied

3/17/2025 at 2:53 PM

Your OpenSSL is connecting via TLS 1.3 -- is your server connecting using the same encryption?

I'm pretty sure that version of SM is on .NET Framework, which is bound to underlying OS TLS limitations - and 2008R2 doesn't support TLS 1.3 - OpenSSL uses it's own internal code so it's not reliant on the underlying OS.

MailEnable survivor / convert --

Tom Replied

3/19/2025 at 9:43 AM

Thanks for the hint.
Indeed, 2008R2 only supports TLS 1.2. But testing via openssl limited to TLS 1.2 is working fine, connection is ok and retrieving email is possible !
openssl s_client -crlf -tls1_2 -connect pop.isp.be:995 -brief
CONNECTION ESTABLISHED
Protocol version: TLSv1.2
Ciphersuite: ECDHE-RSA-AES256-GCM-SHA384
Peer certificate: C = BE, ST = Brussels Hoofdstedelijk Gewest, L = Schaarbeek, O = Proximus NV, CN = pop.isp.be
Hash used: SHA256
Signature type: RSA-PSS
Verification: OK
Supported Elliptic Curve Point Formats: uncompressed:ansiX962_compressed_prime:ansiX962_compressed_char2
Server Temp Key: ECDH, prime256v1, 256 bits
+OK InterMail POP3 server ready.
user userid@isp.be
+OK please send PASS command
pass *********
+OK userid@isp.be is welcome here
stat
+OK 9 832384

So it seems the encryption is not the problem ?
Is there a way to verify what encryption SM is really using ?
Or getting a more detailed SM error log than "Could not understand servers response to connection" ?

Kyle Kerst Replied

3/19/2025 at 11:58 AM

Employee Post

SmarterMail will use whichever versions of TLS are mandated at the OS level, unless you override them in SmarterMail directly which you can do in Settings>Protocols>Security Protocols. Setting the versions used at the Windows level can be done with utilities like IISCrypto from Nartac Software.

Kyle Kerst

Lead Internal Network/System Administrator

SmarterTools Inc.

smartertools.com

Tom Replied

3/20/2025 at 8:59 AM

Hi Kyle,
It seems SM v16 has no Settings>Protocols>Security Protocols ?
At Settings>Protocols there's only an option for SMTP Out 'Enable TLS if supported by the remote server' being switched on.
But no settings for POP or IMAP or in general.
The Windows IIS server supports TLS 1.2, being confirmed by testing via www.ssllabs.com/ssltest.
So still no clue why POP retrieval is not working anymore ...

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