Email delivery problems rarely show up as an obvious outage — mail just quietly lands in spam, or bounces, or never arrives. Most of the time the root cause is SMTP configuration that was never fully finished. Here’s what actually matters.
Authentication: SPF, DKIM, and DMARC
These three DNS-based records are the foundation of deliverability. SPF declares which servers are allowed to send mail for your domain. DKIM cryptographically signs outgoing mail so receivers can verify it wasn’t altered in transit. DMARC tells receiving servers what to do when SPF or DKIM checks fail, and gives you visibility into who’s sending mail claiming to be from your domain. Missing any one of these significantly increases the odds of landing in spam.
Reverse DNS and IP Reputation
Sending mail from an IP address without a matching reverse DNS (PTR) record is one of the fastest ways to get flagged. A fresh IP with no sending history also starts with limited trust — this is why “IP warm-up” (gradually increasing send volume) matters for anything beyond low-volume transactional mail.
TLS and Port Configuration
Modern SMTP should use STARTTLS or implicit TLS (port 465) rather than unencrypted port 25 for submission. Misconfigured or expired TLS certificates on a mail server are a common, easily-missed cause of intermittent delivery failures.
Queue and Bounce Handling
A production mail server needs a real bounce-handling strategy — hard bounces should stop future sends to that address, and soft bounces need a sane retry policy. Without this, sending reputation degrades over time even if the initial configuration was correct.
Where We Come In
Our SMTP Email Server Configuration service covers exactly this — authentication records, TLS, reputation setup, and ongoing hardening — so mail delivery is a solved problem, not a recurring investigation. Reach out if your mail is landing in spam and you’re not sure why.