2. Connect Mail Server
Step 2 of the Conbool connection. Pick the mail server variant and connect it to Conbool.
What happens here: The mail server is configured so that outbound emails flow through Conbool and inbound messages are accepted from Conbool.
Prerequisite: Step 1 Domain & DNS Setup is complete and all four DNS checks are green.
Effort: 5 minutes for Microsoft 365 via wizard click, 30 to 60 minutes for manual setup.
Which Variant Matches the Mail System?
| Mail system | Guide | Effort |
|---|---|---|
| Microsoft 365 or Exchange Online | Exchange Online for Microsoft 365 | 5 minutes via wizard, or 30 minutes manually |
| Local Exchange server, version 2016 or later | Exchange On-Premises | 15 to 25 minutes manually |
| Open-Xchange, OX App Suite or OX Mail | Open-Xchange | 30 to 60 minutes manually |
| Postfix, Sendmail, Zimbra, Kerio and others | SMTP Relay | 30 to 60 minutes manually |
Microsoft 365 is the only case where the Setup Assistant rolls out the complete mail server configuration automatically (via Microsoft Entra Admin Consent). All other variants are configured on the mail server itself. In the Setup Assistant, the mode Manual configuration is chosen and the relay host entered.
Scope (Exchange Online, auto mode): During automatic deployment for Exchange Online, the scope of the Conbool transport rule can be limited to individual senders or a Microsoft 365 group. Only the chosen mailboxes use Conbool, without touching DNS or MX. Details see Exchange Online for Microsoft 365 → Routing Rule Scope.
What All Variants Have in Common
Regardless of the target system, three points are always the same:
- Outbound. The mail server forwards all outbound messages to
mail.conbool.com. With required TLS and certificate validation againstmail.conbool.com. - Inbound. The mail server accepts SMTP connections from the Conbool IP addresses, also with mandatory TLS. Conbool provides the IP list.
- Loop protection. On Exchange Online, the Conbool transport rule uses the header
X-Conbool-<YourDomain>: trueto prevent already-processed messages from looping back through Conbool. On On-Premises and SMTP-Relay systems no loop occurs by design, because routing runs via the Send Connector or smart host and returns from the Conbool mailer go directly to the local mailbox.
The variant-specific guide shows these three points in the actual language of the respective system, that is connector in the Exchange Admin Center, smart host in Postfix, and so on.
Done When
The connection test in the Setup Assistant reports "SMTP reachable". The connection is complete and the wizard can be finished with Finish.
→ Continue with the connection test and completion in the Setup Assistant.