Dedicated sending hosts
Mail transfer agents on dedicated IP addresses, with reverse DNS matching the hostname announced on every connection.
The service
Port Twentyfive operates dedicated outbound mail transfer infrastructure. We run our own sending hosts on dedicated addresses rather than relaying through shared third-party infrastructure.
That distinction matters because it determines who is accountable. On shared infrastructure, delivery outcomes are a function of everyone else's behaviour and the operator's abstractions sit between you and the truth. Running the transfer agent directly means authentication, delivery policy, retry behaviour, throttling and complaint handling are configured by us and answerable to us, and every delivery attempt is recorded with the receiving server's verbatim response.
Infrastructure
Authenticated mail
SPF, DKIM and DMARC alignment on all outbound mail, TLS in transit, and published MTA-STS and TLS reporting policy.
Complete delivery logging
Every attempt records the receiving server's response verbatim, including deferrals and soft failures, so delivery problems are diagnosed rather than guessed at.
Complaint handling
Registered with the major feedback loops. Complaints are actioned against a global suppression list and investigated at source.
Reputation monitoring
Continuous monitoring of per-address complaint rate, blocklist status and inbox placement. Sending pauses automatically on material deviation.
Rate and volume control
Per-destination connection limits and delivery rates, tuned to each mailbox provider's published guidance and observed behaviour.
Sending policy
Every message leaving this infrastructure carries accurate sender identification, a working reply address, a valid postal identity and a one-click unsubscribe header conforming to RFC 8058.
Unsubscribe requests are honoured within 48 hours and applied across every sending domain we operate, not only the one that generated the request. Suppression is permanent and survives list re-imports.
Complaint rate is monitored continuously and held well beneath the 0.30% threshold published by the major mailbox providers. Any sustained deviation pauses sending on the affected address and domain until it is investigated and resolved.
Contact
| abuse | abuse@porttwentyfive.com Monitored. Reports are investigated and the sending address suppressed. |
|---|---|
| postmaster | postmaster@porttwentyfive.com Deliverability and technical correspondence from mailbox providers. |
| security.txt | /.well-known/security.txt Machine-readable contact record, RFC 9116. |
| sending host | mta1.porttwentyfive.com |
For mailbox operators
If mail from this infrastructure is causing you a problem, write to abuse@porttwentyfive.com and we will act on it. We would rather hear from you directly than be filtered silently.
Rate limiting requests, delivery policy questions and reports of misconfiguration are welcome at the same address and are read by a person.