Why your outbound mail might not be arriving

If your own server sends mail directly, several common problems can quietly sink your deliverability:

• Poor IP reputation — if Spamhaus, Barracuda or Microsoft SNDS list your IP (or its neighbourhood), Gmail quietly spam-folders your mail and Microsoft outright rejects it.
• Blocked port 25 — most consumer and many business ISPs block outbound port 25, so your server can't talk to the world directly at all.
• Dynamic or shared IP — residential, shared-hosting or NAT-pool IPs are treated as low-trust by default.
• Missing PTR, SPF or DKIM — without proper reverse DNS, aligned SPF and a DKIM signature, modern receivers treat your mail as spam.

Smarthost sidesteps all of these by handing your mail to reputable relay IPs that receivers already trust.