Missing or mismatched PTR
An IP without reverse DNS, or with a PTR that doesn't resolve back to it, looks like a compromised machine and is often rejected.
Warm-up by provider
How to warm up a Corporate SMTP inbox
Short answerTo warm up mailboxes on your own SMTP server, make sure every sending IP has a matching PTR record and TLS, publish SPF, DKIM and DMARC, connect each mailbox over IMAP and SMTP, and ramp from 2-5 to 30-50 emails a day. On your own server you own the IP's reputation too, so the ramp warms the IP as well as the domain.
Step by step
Connect SMTP to RoxInbox
Connection method: IMAP/SMTP.
- 1
Confirm the server's sending IPs have PTR records that resolve back to the same IP, and that TLS is enabled.
- 2
Publish SPF (including the server's IPs), DKIM and DMARC for the domain.
- 3
In RoxInbox, choose Add mailbox, then Custom SMTP, and enter the IMAP and SMTP host, port and credentials.
- 4
RoxInbox tests both connections, checks DNS and blocklists, and starts the ramp.
Sending limits 2026
SMTP sending limits
With your own server there's no provider ceiling, which makes it easy to send too much too soon. A new IP needs warming just like a new domain.
| Limit | Value |
|---|---|
| Sending limits | Set by your server's administrator |
| What receivers check | PTR (reverse DNS), TLS, SPF, DKIM, DMARC and the IP's own reputation |
Ramp plan
A starting ramp for a new domain.
RoxInbox adapts this daily from real spam signals. Use the calculator for a plan for your own domain.
| Week | Emails per day | Note |
|---|---|---|
| Week 1 | 3-8 | Warm-up only; watch for blocklist listings |
| Week 2 | 8-18 | Check PTR and TLS at every receiving provider |
| Week 3 | 18-35 | Placement test across all providers |
| Week 4 | 35-50 | Start campaigns slowly |
Pitfalls
What sends SMTP mail to spam
A new IP with no history
A fresh IP has no reputation. Ramp it gradually, and check blocklists before you start; recycled IPs may carry old listings.
Open relay or weak auth
A misconfigured server can be abused by spammers within hours, and your IP's reputation goes with it.
FAQ
SMTP warm-up questions
Do I need to warm up a new dedicated IP?
Yes. A new IP has no reputation with any provider. Ramp volume gradually and keep authentication and PTR correct from day one.
How do I check my server's PTR record?
Run the free domain health check: it looks up PTR records for your mail servers and checks that each one resolves back to the same IP.
Other providers: Outlook / Microsoft 365 · Google Workspace · Yahoo Mail · Zoho Mail · iCloud Mail · Mail.ru · Yandex Mail · GMX / WEB.DE
Warm up SMTP on autopilot.
RoxInbox connects in five minutes, checks your DNS first, and shows placement at every provider.