What it is
The IMP Blacklist is maintained by SWITCH, the Swiss national internet registry and academic network operator. It covers IP addresses identified as sending spam or as infected with email worms within the Swiss academic and research network infrastructure.
How it affects SMTP delivery
IMP is used primarily within Swiss and European academic mail environments. A listing here mainly affects deliverability to .ch academic domains and institutions using SWITCH's mail infrastructure.
What causes a listing
Listings occur from spam trap hits on SWITCH-monitored addresses or from detection of worm-generated mail from your IP.
How to get removed
Contact SWITCH via their abuse contact or the IMP portal to request removal.
For the full reference catalog, see the email blocklist directory.
Delisting process in detail
The IMP blocklist (Internet Mail Protection) targets observed spam sources. Delisting is handled through the operator’s portal and typically requires documenting remediation of the underlying abuse. Response times vary based on operator availability, usually within 24-72 hours for well-documented requests. Automatic decay occurs when the observed spam pattern stops. IMP is a mid-scale blocklist with regional and specialty focus rather than global deployment.
Prevention practices
IMP prevention follows standard anti-abuse fundamentals. Authentication (SPF, DKIM, DMARC), disciplined list hygiene (double opt-in, prompt bounce suppression), and complaint monitoring remain the primary defenses. Because IMP is a smaller list, its impact is limited to receivers that specifically query it. Monitor IMP alongside major public blocklists for comprehensive coverage. Gradual IP warmup and consistent send patterns matter as elsewhere.
Common listing causes
IMP listings correlate with observed spam patterns from the listed IP. Common causes include purchased lists that hit IMP honeypots, compromised shared-hosting accounts, and volume spikes without proper warmup. Because IMP operates a smaller honeypot network than major blocklists, listings often reflect specific abuse patterns rather than broad reputation issues, making them easier to identify and remediate.
Related blocklists
IMP operates alongside other mid-scale blocklists and provides regional or specialty coverage. Enterprise reputation monitoring combines IMP with major blocklists (Spamhaus, Barracuda, SpamCop) for comprehensive coverage. Because smaller blocklists sometimes react faster to specific patterns, they can provide early-warning signals; however, for most senders, monitoring the major public blocklists provides sufficient signal.
About the Author
Alaa · LinkedIn
Email infrastructure specialist with 8+ years of hands-on experience in SMTP, deliverability, and email verification. I’ve configured and troubleshot mail systems across Postfix, Exchange, and cloud relays, managed IP reputation and warmup campaigns, and built verification pipelines processing millions of addresses. My work spans DNS authentication (SPF, DKIM, DMARC, BIMI), bounce handling, blocklist monitoring, and compliance frameworks including CAN-SPAM and GDPR. I write every article on SMTPedia to give email professionals, developers, and marketers the accurate, RFC-grounded reference they need.
About SMTPedia
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