New IPs need warm-up; send gradually and follow best practices. Monitor bounces, spam complaints, and blacklists. Use SPF, DKIM, DMARC. Dedicated IPs help when you control volume and content.
Warm-up and volume
- New IPs: Have no reputation. Sending large volume immediately can trigger filters or blacklisting. Warm up: start with low volume (e.g. hundreds per day), increase over days or weeks. Let receivers see consistent, legitimate traffic.
- Gradual increase: Do not double volume overnight. Spread growth; monitor bounce and complaint rates. If you see a spike in bounces or spam reports, slow down or fix content/list quality.
- Dedicated vs shared: Dedicated IPs let you build your own reputation. Shared IPs (e.g. with other tenants) can be hurt by others' bad behavior. For high volume or critical deliverability, dedicated IPs are often worth it—if you control content and follow best practices.
Best practices
- List quality: Send only to engaged, opted-in addresses. Remove bounces and unsubscribes promptly. Do not buy lists or send to old/untested addresses (spam traps).
- Content: Avoid spammy words, all caps, excessive links, or misleading subject lines. Use plain text or well-formatted HTML; test with mail-tester or similar. Authenticate (see below).
- Consistency: Sending pattern (volume, frequency) and content should be consistent. Sudden changes can trigger filters.
Authentication: SPF, DKIM, DMARC
- SPF: DNS record listing which servers can send for your domain. Receivers check that the sending IP is in the list. Reduces spoofing and improves trust.
- DKIM: Sign messages with a private key; publish public key in DNS. Receivers verify the signature. Proves the message was not altered and came from your domain.
- DMARC: Policy (DNS) telling receivers what to do with messages that fail SPF/DKIM (none, quarantine, reject). Use
p=noneinitially to collect reports; thenp=quarantineorp=rejectonce you are confident. Reports help you find spoofing and misconfigurations.
Monitoring
- Bounces: Hard bounces (invalid address) — remove immediately. Soft bounces (mailbox full, temp failure) — retry with backoff; remove if persistent.
- Spam complaints: Track complaint rate (complaints / delivered). High rate hurts reputation. Investigate and fix content or targeting.
- Blacklists: Check your IP(s) on major blacklists (e.g. Spamhaus, SORBS). If listed, follow the list's delisting process (fix the cause first—e.g. stop sending to spam traps, fix auth).
- Deliverability tools: Use seed lists, inbox placement tests, or services (e.g. Mail-tester, GlockApps) to see how you land. Fix issues before scaling.
Summary
New IPs need warm-up; send gradually and follow best practices. Monitor bounces, spam complaints, and blacklists. Use SPF, DKIM, DMARC. Dedicated IPs help when you control volume and content; keep list and content clean.
