Knowledge Base

Frequently asked questions and troubleshooting guides for all Servolutions products. For the broader questions — POP3 retrieval into Exchange, send connectors and smart hosts, sender addresses in Outlook, OAuth2 — see the Exchange mail flow guides. The SMTP replies Exchange returns to a connector — 421 4.4.1, 421 4.4.2, 451 4.7.0, 452 4.3.1, 530 5.7.1, 550 5.7.1 and the rest — are collected on one page in Exchange SMTP error codes explained.

POPcon and POPcon PRO

Exchange Server Configuration Guides

• Configuration of Exchange 2013 or 2016 Server
• Configuration of Exchange 2010 Server
• Configuration of Exchange 2007 Server
• Configuration of Exchange 2003 Server
• Configuration of Exchange 2000 Server
• Configuration of Exchange Server 5.5

Frequently Asked Questions

• How can I transfer my POPcon configuration settings to a new server?
• How to connect to Gmail with modern authentication / OAuth2
• Connect to Microsoft 365 or Outlook online accounts with OAuth2
• "530 5.7.1 Client was not authenticated" error from Exchange
• Exchange does not accept emails larger than 10 MB — how to increase the limit
• "452 4.3.1 Insufficient system resources" error from Exchange
• "550 5.7.1 Unable to relay" error from Exchange
• There are .msg files in the POPcon folder with undistributed emails — how to redistribute them
• Exchange 2013 SMTP error "451 4.7.0 Temporary server error. Please try again later. PRX"
• Emails to unknown Exchange recipients remain stuck in POPcon's queue
• Does POPcon work with Exchange 2010, 2007, 2003, 2000, 5.5, SBS editions?
• Emails from a mailing list are not distributed correctly
• All emails get forwarded to the postmaster because they "do not have local recipients"
• POPcon hangs when my virus scanner deletes infected .msg files
• Can I trigger mail retrieval from the command line?
• Why are emails to unknown recipients in my domain not forwarded to the postmaster?
• POPcon downloads email fine but cannot reach my Exchange server
• BCC recipients do not receive the email — TO: and CC: recipients do
• How to configure POPcon to work with an ISA Server (proxy)
• "554 5.5.2 No valid recipients" error from Exchange
• POPconAdmin does not work or cannot communicate with the POPcon service
• Will I lose emails if Exchange is down when POPcon tries to deliver?
• Is there a log of POPcon's actions — where can I find it?
• How to get rid of emails stuck in POPcon's delivery queue
• All emails are suddenly tagged as SPAM after working fine for a long time
• POPcon does not install on my machine — alternative installation method
• Exchange SMTP connection unexpectedly closed, or "454 5.7.3 Client does not have permission to submit mail"
• How to resend already-downloaded messages
• Configuring POPcon for a branch office that handles only part of a domain
• How to diagnose malfunctioning antispam blacklist server lookups
• "Mail transfer to Exchange failed: Connection to host denied"
• "550 5.7.1 Requested action not taken: message refused" from Exchange
• POPcon delivers email to both the real recipient AND a catch-all mailbox name
• POPcon says it "drops copies" of downloaded email — what does this mean?
• "550 5.5.1 user unknown" or "503 5.5.2 need Rcpt command" from Exchange
• Can POPcon download email from AOL accounts via IMAP?
• Can POPcon download email from Gmail accounts?
• "Out of Office" replies go to internal users but not to external internet senders
• Why does POPcon need to know the "accepted domains" on the POP3/IMAP config tab?
• How to enable non-delivery reports (NDRs) for external senders in Exchange 2003
• Mail does not reach mail-enabled public folders
• Only messages under 10 MB come through — does POPcon impose a size limit?
• Windows Data Execution Prevention (DEP) is crashing the POPcon antivirus engine
• "530 5.7.0 Must issue a STARTTLS command first" or similar STARTTLS error from Exchange
• Spam checking takes 30 seconds per message — why is it so slow?
• "[blacklist] could not be tested and will not be used" — what does this mean?
• Emails to mail-enabled public folders arrive as "posts" instead of emails
• How does the POPcon PRO antispam feature work, and why is it not 100% accurate?
• Can I use wildcards like `*@spammer.com` in the anti-spam blacklist?
• What is the shortest mail download interval POPcon supports?
• POPcon moved emails to TOOLARGE or BADMAIL folders — how to resend them
• "421 4.4.1 Connection timed out" from Exchange 2007
• Exchange 2007 only accepts one or a few messages at a time from POPcon
• "Exchange aborted receiving the message after N bytes" error
• Why does my distribution group not accept emails from external senders?
• How to forward some accounts to a non-local mailbox on the internet
• "552 5.3.4 Header size exceeds fixed maximum size" from Exchange
• How to have non-delivery reports (NDRs) sent for unknown users
• "421 4.4.2 Message submission rate for this client has exceeded the configured limit"
• How to have NDRs sent for emails that are too large instead of moving them to TOOLARGE
• "Could not reach Exchange SMTP server — check that IP port 25 is not blocked"
• "530 SMTP authentication is required" — what does this mean?
• IONOS blocks non-delivery reports and out-of-office messages
• I installed CSCatchAll and configured a catch-all account but it does not seem to work at all! What can I check?
• How do I configure CSCatchAll? The Administrator utility only allows me to enter a license code.
• How to protect Wordpress sites with BotFence
• MultiSendcon service won’t start after upgrading — "ChilkatDotNet47.dll or one of its dependencies could not be found"

ChangeSender

• ChangeSender is installed but the sender address is not changing
• How to restrict users' choices for Send-As addresses in ChangeSender
• How to use the same sender address for two Exchange mailboxes
• How to disable the ChangeSender add-in for all users in a terminal server / Citrix environment

MultiSendcon

• "504 5.7.4 Unrecognized authentication type" when using Office 365 SMTP relay
• How to manually create the MultiSendcon Send Connector in Exchange

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