Spam Folder vs Quarantine
Spam folder placement and quarantine placement are two different fates for suspect mail. Spam folder is recipient-visible (they can dig it out). Quarantine is administrator-controlled; the recipient usually doesn't know the message arrived. Quarantine is more common on enterprise tenants and is much worse for deliverability.
The recipient's mailbox provider decides where suspect mail goes. The decision has very different implications for the sender.
Spam folder placement
- Visible to the recipient
- Recipient can mark "not spam" and pull the message back
- Recipient activity influences future sender reputation
- Standard on consumer providers (Gmail, Yahoo, Apple)
Quarantine placement
- Invisible to the recipient (in most configurations)
- Administrator must release the message
- Recipient typically never sees the message
- Common on Microsoft 365 enterprise tenants with Defender, Mimecast, Proofpoint policies
Deliverability implications
- Spam folder: recoverable with engagement and reputation work
- Quarantine: much harder to detect; sender often doesn't know the messages are being quarantined
- Aggressive enterprise quarantine policies can drop B2B inbox rate 20-40% on a single Microsoft 365 tenant
How to detect quarantine placement
- Seed-list testing across enterprise tenants
- Microsoft SNDS (Smart Network Data Services) for Microsoft 365
- Direct outreach to known recipients ("did the message arrive?") when other diagnostics fail
Frequently asked questions
Can I appeal a quarantine decision?+
Indirectly. Reach out to the recipient's IT department; they can whitelist your sending domain or specific addresses.
Does Outsolvi tracking detect quarantine?+
Quarantined messages produce zero open events because the recipient never sees them. Sustained zero-engagement patterns on previously-engaged recipients is a quarantine signal worth investigating.
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We update these pages when the underlying mechanics change. new mailbox-provider rules, new tracker behavior, new measurement gaps. The dates above are real revisions, not auto-touches.