SMTP relay vs. your own mail server: when each makes sense

Reviewed by: Holger D. Erbe, Managing Director of LOGIN SystemHaus GmbH Published: August 2, 2026 Last reviewed: August 28, 2026

Your own mail server costs nothing in licenses and is installed in an hour. That is exactly why people underestimate it. This article does the math on what it really takes and says when it is still the right choice.

What a mail server really costs

The software is free, and the virtual server costs a few euros a month. The math still rarely works out, because the expensive part is labor, and that does not come with the setup but afterwards.

Email that reliably reaches the inbox needs an IP address with a good reputation. You do not build that reputation through configuration but through months of steady sending without complaints. If you take a fresh address from a data center block, the big mailbox providers will treat it with suspicion from the start, and you only find out when your invoices are sitting in the spam folder.

The five tasks nobody plans for

• Building and keeping a reputation. Ramp up volume slowly, watch the complaint rate, find the cause when delivery drops.
• Monitoring blacklists. There are dozens of them, they do not notify you, and a listing gets noticed by your customer first, not by you.
• Processing bounces and suppressing addresses. Done by hand, it gets forgotten after two weeks, and that is exactly when the bounce rate climbs.
• Rotating DKIM keys, reading DMARC reports. Neither is a one-time setup. Both are ongoing maintenance.
• Installing security updates. A mail server is reachable from the internet. An open relay gets found within hours.

Realistically, that adds up to a few hours a month over the year, unevenly spread: nothing for a long time, and then a day when you get nothing else done. If you have that time and enjoy the subject, you will do fine. If you do not, you pay for it anyway, just in the form of undelivered email.

When your own server is still the right choice

There are good reasons to run it yourself, and they rarely have anything to do with money:

• The content must not leave your premises on a technical level, for example with special categories of personal data or contractual requirements.
• You already have someone who knows how to run mail and actually does it. Then the additional effort is small.
• Sending volume is very small and purely internal, such as system alerts to three addresses in your own company.
• Protocol edge cases that no service supports.

“We already have a server” is not a good reason. Running mailboxes and delivering mail to the outside world are two different jobs, and only the second one is hard.

The middle ground most people overlook

Your own mail server and a relay are not mutually exclusive. The common and usually best setup: mailboxes, distribution lists and internal delivery stay where they are, and the server no longer delivers outbound mail itself but hands it to a relay. In Postfix that is one line (relayhost), in Exchange a send connector.

That way you keep control over content and mailboxes and hand off exactly the part that needs constant upkeep: reputation, blacklists, retries. Your sender domain stays the same, and recipients see no difference.

Decision guide

What switching means in practice

Moving from your own server to a relay is not a project. You add the sender domain at the service, verify it with a DNS record, add SPF and DKIM and enter the relay host and credentials in your mail server. The only delay to plan for is DNS propagation of up to 24 hours. What the records look like in detail is covered in the guide to SPF, DKIM and DMARC, and the steps in the portal are shown in the Getting started guide.

Switching back is just as easy. A relay does not lock you in: your mailboxes are not there, the domain belongs to you, and there is no data format you would have to migrate out of.

A sample calculation, done honestly

A midsize business sends 8,000 emails a month: invoices from the ERP system, order confirmations from the online store, the occasional newsletter to existing customers.

The server price is lower, the total cost is not. Two hours of admin time a month cost more than the difference, and that is the optimistic case. The pessimistic one is the day a blacklist hits and your invoices do not go out.

The reverse is also true: at 80 emails a month, all to internal recipients, the math looks different, and there is little reason not to use the server you already have.

Five questions before you decide

1. Who deals with it when something breaks? If the answer is “we'll see,” running your own is not an option.
2. How bad is a day without sending? For invoices and order confirmations, the answer is usually unpleasant.
3. What does your address list look like? Old, neglected lists ruin any reputation, no matter which route they are sent through.
4. Do you have a static IP with a sending history? A fresh address from a data center block starts at a disadvantage.
5. Are there requirements that dictate the route? Then cost is not what decides.