Every mail server goes down occasionally. A hardware failure, a software update, an ISP outage, a maintenance window — any of these can make your primary mail server temporarily unreachable. Without a backup plan, inbound email sent during that window bounces back to the sender with a permanent or temporary failure notice. Mail bagging prevents that from happening.
What Mail Bagging Is
Mail bagging is the practice of configuring a secondary mail server — typically operated by a third party like Infinity Data Center — to accept and hold inbound email when your primary mail server is unreachable. The secondary server acts as a temporary holding area, or "bag," for messages that cannot be delivered to the primary destination. When your primary server comes back online, the secondary server delivers everything it collected, in order, automatically.
The term "mail bagging" is an older industry colloquialism for what is now more commonly called MX backup, secondary MX, or email spooling. All of these terms describe the same fundamental concept. Infinity Data Center's mail bagging and MX backup service is called StrataMX Backup.
How Mail Bagging Works
Mail bagging relies on the DNS MX record system. When someone sends you an email, their mail server performs a DNS lookup for your domain's MX (Mail Exchange) records. MX records list every server that accepts inbound mail for your domain, each assigned a numeric priority. Lower numbers have higher priority — the sending server always tries the lowest-priority-number server first.
Mail bagging works by adding a second MX record with a higher priority number than your primary server. Under normal conditions this record is never used — all mail goes directly to your primary. The moment your primary becomes unreachable, sending servers automatically try the next MX record in the list — which is your mail bagging server. Mail is accepted there and held.
MX Record Priority and Fallback
Here is what the DNS configuration looks like with mail bagging enabled:
yourcompany.com MX 10 mail.yourcompany.com (primary — highest priority) yourcompany.com MX 20 stratamx.infinitydatacenter.com (mail bagging — fallback)
Priority 10 is tried first. If the primary (priority 10) is reachable, every message goes there. If the primary is unreachable — connection refused, timeout, SMTP error — the sending server automatically tries priority 20. StrataMX Backup accepts the message, acknowledges delivery to the sending server, and queues it for later relay to the primary.
This fallback is built into the SMTP standard. Every mail server on the internet implements it automatically. No special configuration is required on the sending side — the fallback happens transparently for every sender in the world.
Queue Retention Windows
Mail bagging services hold queued messages for a defined retention window — the maximum period mail will be held before expiring. StrataMX Backup provides up to 30-day queue retention, meaning even extended outages are fully covered without mail loss.
During the retention window, the mail bagging server retries delivery to the primary at regular intervals — typically every 5 minutes once the primary server is detected as available again. The retry logic is automatic. When the primary comes back online, the queue drains in order within minutes.
| Scenario | Primary Down | Mail Bagging Response | User Impact |
|---|---|---|---|
| Planned maintenance (2 hours) | 2 hours | Accepts and queues all inbound mail | None — mail arrives on recovery |
| ISP outage (12 hours) | 12 hours | Accepts and queues all inbound mail | None — mail arrives on recovery |
| Hardware failure (3 days) | 72 hours | Accepts and queues all inbound mail | None — mail arrives on recovery |
| Extended migration (7 days) | 7 days | Accepts and queues all inbound mail | None within retention window |
Mail Bagging vs. Email Continuity
Mail bagging and email continuity are related but solve different problems. Understanding the distinction helps you choose the right level of protection for each customer or deployment.
Mail bagging (MX backup / email spooling) is a passive protective layer. It ensures inbound email is captured and delivered on recovery. Users cannot access queued messages during the outage — the mail is simply held safely until the primary comes back. Mail bagging answers the question: will my mail be lost if my server goes down? The answer becomes no.
Email continuity is an active layer that goes further. When the primary server goes down, continuity gives users immediate access to a live emergency mailbox — they can read new inbound messages, reply, compose, and send email normally through a branded webmail portal. Mail bagging protects the queue; continuity keeps people working. StrataMail Continuity provides both simultaneously — dual delivery stores messages locally for webmail access and queues them for relay to the primary.
When You Need Mail Bagging
Mail bagging is appropriate for any environment where inbound email loss during a server outage is unacceptable. Specific scenarios where it provides immediate value:
- Self-hosted mail servers — on-premise Exchange, Postfix, Zimbra, SmarterMail — where maintenance windows and hardware failures create real downtime risk
- Hosted email with planned downtime — cPanel/WHM migrations, version upgrades, server moves — where the mail server will be intentionally offline
- Microsoft 365 tenant-to-tenant migrations — DNS propagation during M365 cutover can route inbound mail unpredictably; mail bagging captures everything regardless of DNS state
- ISP redundancy gaps — organizations with a single upstream internet connection where ISP outages knock out inbound SMTP delivery
- Any organization that has bounced email during an outage — once it has happened, the cost of mail bagging is immediately obvious
Mail Bagging for MSPs and Resellers
For MSPs and hosting providers, mail bagging is one of the easiest value-add services to offer across an entire client base. StrataMX Backup uses per-domain pricing — no per-mailbox or per-user fees — so a reseller can protect every customer domain under management for a flat monthly cost that scales with their portfolio.
The reseller platform is white-labeled: your branding appears on the admin interface and all customer-facing communications. Outage alerts are sent from your email address. Your customers see your brand, not Infinity Data Center's. WHMCS billing integration is included for automated provisioning and invoicing.
Reseller tiers start at $29.99/month for 5 domains ($6.00 effective per domain) up to $149.99/month for 50 domains ($3.00 effective per domain). SpamWeeder Premium integrates natively — when SpamWeeder is active as the primary MX filter, its built-in multi-destination failover automatically routes to StrataMX Backup when a primary server goes down, with no secondary DNS MX record needed.
Contact us to discuss adding mail bagging to your reseller portfolio, or call 866.790.4678. You can also view full reseller pricing on the IDC website.