Exchange mail flow guides › Inbound: POP3 and IMAP retrieval
The SBS 2008/2011 POP3 Connector: what it did, its limits, and the replacement for Exchange 2016 to SE
The Windows SBS 2008 and 2011 POP3 Connector downloaded mail from external POP3 mailboxes and delivered it to an Exchange user or distribution group; Microsoft never shipped it for standalone Exchange, so shops that leave SBS need a separate connector service. This guide lists what the SBS connector did, where it stopped, how a current POP3/IMAP connector compares, and how to switch without losing a message.
Updated on 2026-09-12
What the SBS POP3 Connector did
Microsoft’s documentation for the Windows SBS 2008 POP3 Connector describes a small but complete feature. Each external POP3 mailbox was entered on the Accounts tab of the connector’s properties page in the Windows SBS Console and mapped to one SBS user account or one distribution group. The Scheduling tab set how often mail was retrieved, with a button to retrieve it immediately. The connector could connect over SSL and authenticate with Basic, SPA or APOP. It handed every downloaded message to Exchange over SMTP, so Exchange’s own antispam agent scanned it and moved spam to a badmail folder under the SBS data directory. Errors went to the Windows SBS event log.
Two design decisions shaped a decade of small-business mail: replies to a message collected by POP3 were sent out through the local Exchange server, never back through the provider’s POP3 server; and messages larger than 10 MB were not retrieved at all, because the SMTP path into Exchange was limited to 10 MB. The connector logged an event and left the message at the provider for you to download or delete by hand.
SBS POP3 Connector vs. a current POP3/IMAP connector
The right-hand column describes POPcon, the connector service most SBS shops move to; the feature pages for POP3/IMAP accounts and scheduling hold the details.
| SBS 2008 / 2011 POP3 Connector | POPcon on Exchange 2013 to SE | |
|---|---|---|
| Mailbox mapping | One POP3 mailbox delivers to one SBS user or one distribution group | Single-user mailbox to one recipient, or catch-all mailbox split by the recipient headers, with accepted recipient domains and a re-route address for unresolved recipients |
| Protocols | POP3 | POP3, POP3-SSL, IMAP and IMAP-SSL (default ports 110, 995, 143, 993) |
| Encryption | SSL to the POP3 server where the provider supports it | TLS 1.2 / 1.3 on POP3 and IMAP connections |
| Authentication | Basic, SPA, APOP | Password, plus OAuth 2.0 (modern authentication) for Microsoft 365 IMAP and Gmail mailboxes |
| Messages over the Exchange size limit | Not downloaded; an event asks you to download or delete the message manually or raise the Exchange limit | Downloaded; if Exchange refuses the message it waits in the TOOLARGE folder and is resent through the PICKUP folder after the limit is raised, or Exchange sends the sender an NDR |
| Retrieval schedule | Interval set on the Scheduling tab, or retrieve immediately | Fixed interval down to 1 minute, 0 for continuous retrieval, or exact times per weekday |
| Spam and viruses | Exchange antispam agent after SMTP submission; spam to the badmail folder | Exchange still scans on receipt; POPcon PRO adds RBL blacklist checks and antivirus scanning before the message reaches Exchange |
| Where it runs | On the SBS server only, managed in the Windows SBS Console | As a Windows service on Windows Server 2012 to 2025 or Windows 7 to 11, on the Exchange server or on a separate machine (requirements) |
| Exchange versions served | The Exchange 2007 (SBS 2008) or Exchange 2010 (SBS 2011) inside the same SBS installation | Exchange 5.5 to 2019 and Exchange Server SE, all SBS editions, and other SMTP servers (version list) |
| Mail left at the provider | Not documented on the Microsoft page | Delete after download, leave indefinitely, or leave for N days so another client can fetch the same mail |
If you are still on SBS 2011, the connector is not the problem
An honest reading of the table is that the SBS connector was adequate for its time: POP3 with SSL, a schedule, and delivery into Exchange. If your SBS 2011 server is still running and the mailboxes arrive, there is no reason to touch the connector today. The reason it gets replaced is that Small Business Server itself is retired: the next server is a regular Windows Server with Exchange 2016, 2019 or Exchange Server SE, and that Exchange has a POP3 service for clients but no connector, as explained in Does Exchange Server have a built-in POP3 connector?. The moment to plan the replacement is the moment you plan the migration off SBS, so that the new server collects mail from day one.
The limits that did hurt in practice are the ones in the table: POP3 only, no IMAP; no OAuth 2.0, which Microsoft 365 and Gmail now expect instead of a plain password; messages over 10 MB stranded at the provider; and delivery to one user or one group per mailbox, which forced a distribution group wherever one provider mailbox served several people. A catch-all mailbox for the whole domain, the setup most small companies actually have at their provider, needs the header-based distribution that the SBS connector did not have.
Replacing the connector when you leave SBS
- Prepare the new Exchange server. Create a receive connector that accepts anonymous SMTP from the connector’s IP address and raise its 10 MB default message size; the steps are in Configuring Exchange 2013 / 2016 to receive mail from POPcon. This is the same preparation any SMTP source needs.
- Install the connector. Download POPcon and install it on the new Exchange server or on any other Windows machine in the network. It runs as a Windows service and is configured with the POPcon Administrator program.
- Re-enter the mailboxes. Take each entry from the SBS Accounts tab and add it as a POP3 or IMAP account in POPcon: server name, login, password, port, and the Exchange recipient for a single-user mailbox. A provider mailbox that receives mail for the whole domain becomes a catch-all account with your domain in the accepted recipient domains list. Enter the Exchange server name on the Exchange tab and a postmaster address on the General tab.
- Keep a safety margin. For the first days set each account to leave mail on the server for a few days. If anything has to be rolled back, the messages are still at the provider.
- Hand over. Stop the SBS POP3 Connector and start the POPcon service. Two connectors polling the same mailbox would each take a share of the mail, so the switch is a stop on one side and a start on the other, not a parallel run. Use Trigger mail retrieval in POPcon Administrator and watch the log window for the first cycle.
- Later moves are a file copy. If POPcon ever has to move to another server, the configuration is one file,
popcon.config, plus theUIDS_*.datlists of already downloaded messages; see transferring the POPcon configuration to a new server.
After the switch nothing changes for the users: mail keeps arriving in the same Exchange mailboxes, and replies still leave through the Exchange send connector, as they did under SBS.
Frequently asked questions
Is the SBS POP3 Connector available for Exchange 2016, 2019 or Exchange Server SE?
No. The POP3 Connector was a component of the Windows Small Business Server console, and Microsoft never shipped it for standalone Exchange. Once the SBS server is retired, a separate connector service takes over: it downloads the provider mailboxes and submits the messages to Exchange over SMTP, which is the same way the SBS connector handed mail to Exchange.
Can I keep the same provider mailboxes when I replace the connector?
Yes. Nothing changes at the provider. The new connector logs in to the same POP3 or IMAP mailboxes with the same server name, login and password; only the machine that collects the mail changes. If you want a safety net during the switch, set the new connector to leave messages on the server for a number of days so that a rollback to the old connector still finds them.
Why did the SBS POP3 Connector not download messages larger than 10 MB?
Because it submitted mail to Exchange over SMTP and the SMTP path in SBS was limited to 10 MB; rather than download a message Exchange would refuse, the connector left it on the provider server and logged an event asking you to download or delete it manually or raise the Exchange limit. A current connector downloads the message and, if Exchange refuses it, keeps it in a TOOLARGE folder from which it is resent once the receive connector limit has been raised.
Do I still need a distribution group to deliver one provider mailbox to several people?
Not necessarily. The SBS connector delivered each POP3 mailbox to one user or one distribution group. With POPcon a single-user mailbox goes to one recipient, and a catch-all mailbox is split by reading the recipient headers of each message, so one provider mailbox for the whole domain reaches every Exchange user directly. Rules that forward, copy or reroute by sender, recipient, subject or attachment name are part of POPcon PRO.
More on inbound mail flow in the Exchange mail flow guides, or in the knowledge base. Auf Deutsch: Der SBS-POP3-Connector: Funktionen, Grenzen und der Nachfolger.