How to Mimecast smtp relay
Published October 12, 2024 · Updated July 16, 2026 · SMTP & Deliverability
Mimecast is best known as an email security and continuity gateway — the layer that filters spam, viruses, and data leaks for large organisations. Part of that platform is an outbound SMTP relay that routes your company's mail through Mimecast's inspection before it leaves. If you need to configure a Mimecast SMTP relay — or you are wondering whether it is the right tool for bulk sending — here is the clear version.
What Mimecast's SMTP relay is for
Mimecast's outbound relay exists for security and compliance, not marketing throughput. Mail from your servers routes through Mimecast, which scans it, applies data-loss policies, and then delivers it. It is excellent at keeping corporate email safe and auditable. It is not designed to be a high-volume marketing sender on a dedicated IP.
How to set up a Mimecast SMTP relay (outbound)
- In the Mimecast Administration Console, define an Authorized Outbound Address or authenticated outbound route for your sending server.
- Point your application or mail server to Mimecast's regional outbound SMTP host on the correct port.
- Authenticate the connection (IP-based or credentialed) so Mimecast accepts your mail.
- Confirm your domain's SPF includes Mimecast so downstream servers trust the route.
Exact hostnames and steps depend on your Mimecast region and plan — check your admin console for the values assigned to your account.
Mimecast vs a dedicated SMTP server
| Job | Mimecast relay | Dedicated SMTP |
|---|---|---|
| Security & compliance filtering | Excellent | Not the focus |
| Bulk / marketing volume | Not designed for it | Unlimited |
| Dedicated sending IP | Shared gateway | Yes |
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Frequently asked questions
Can I send bulk email through Mimecast?
Mimecast's outbound relay is built for security-filtered corporate mail, not high-volume marketing. For bulk campaigns, use a dedicated SMTP server designed for throughput and deliverability.
What port does Mimecast SMTP relay use?
Mimecast uses standard SMTP ports on region-specific outbound hosts. The exact host and port are shown in your Mimecast Administration Console for your account and region.
Should I use Mimecast and a dedicated SMTP together?
Often, yes — Mimecast for secure corporate mail and a dedicated SMTP for bulk/marketing sends. Keeping the two streams separate protects both your security posture and your marketing deliverability.