E mail deliverability is a repute drawback as a lot as a technical one. When your server sends mail from a shared IP deal with, your deliverability rides on each different tenant’s sending habits. One spammer on the identical IP pool can push your reputable e mail into spam folders for weeks. A devoted IP on a devoted server…
The Devoted IP Benefit for E mail
IP Status and Shared Internet hosting Danger
Main inbox suppliers (Google, Microsoft, Yahoo) consider inbound e mail based mostly on the sending IP’s repute historical past. Spam complaints, excessive bounce charges, and recognized spam sources all degrade an IP’s repute rating. On shared internet hosting, you don’t have any management over what your IP neighbors ship.
On a devoted server with a devoted IP, your sending repute is completely yours to construct and keep. A clear IP with constant sending quantity and low grievance charges achieves good deliverability inside 4-6 weeks of warmed-up sending. That repute persists so long as you keep clear checklist hygiene.
IP Warming for New Devoted Servers
Beginning transactional or bulk e mail from a brand-new IP requires a warmup interval. Inbox suppliers are suspicious of a brand new IP immediately sending excessive quantity. The usual method: begin with 500-1,000 emails per day in week one, double weekly for 4-6 weeks, and monitor bounce charges and spam complaints all through.
For organizations sending important transactional e mail (password resets, order confirmations) from day one, keep the brand new IP completely for transactional messages throughout warmup. Maintain bulk or advertising and marketing e mail on a separate IP or service till the first IP is absolutely warmed.
Postfix and Dovecot: The Linux Mail Stack
Structure Overview
Postfix handles SMTP (sending and receiving mail). Dovecot handles IMAP and POP3 (shopper entry to saved mail). Collectively they kind the most typical self-hosted Linux mail stack. Each are mature, well-documented, and run effectively on devoted {hardware}.
For a company with 200 mailboxes and reasonable e mail quantity, the useful resource necessities are modest: Postfix and Dovecot collectively devour beneath 2GB of RAM throughout regular operation, leaving many of the server’s reminiscence accessible for different companies or for a big Dovecot mailbox index cache that speeds IMAP folder operations.
Authentication Configuration: SPF, DKIM, DMARC
These three DNS-based authentication mechanisms aren’t optionally available if you need dependable inbox placement. All three needs to be configured earlier than sending any manufacturing e mail from a brand new server:
- SPF (Sender Coverage Framework): A TXT document in your DNS zone itemizing which IP addresses are approved to ship mail on your area. A strict SPF document with -all (laborious fail) for unauthorized senders reduces phishing utilizing your area.
- DKIM (DomainKeys Recognized Mail): Postfix indicators outbound messages with a personal key. Recipients confirm the signature towards the general public key in your DNS. Opendkim integrates with Postfix and handles key rotation. Use 2048-bit RSA keys; 1024-bit is not ample.
- DMARC (Area-based Message Authentication): A coverage document specifying what receiving servers ought to do when SPF or DKIM checks fail. Begin with p=none to watch failures, then tighten to p=quarantine and finally p=reject when you verify all reputable sending sources are authenticated.
DMARC reporting (rua= tag) sends XML reviews from main inbox suppliers displaying authentication failures. Arrange a DMARC report parser (dmarcian or a self-hosted parser) to evaluation these reviews throughout the first 30 days after launch.
Anti-Spam Configuration
SpamAssassin and Rspamd
SpamAssassin is the standard Linux spam filter, rule-based and extensively deployed. Rspamd is a contemporary different with considerably higher efficiency (handles 1000’s of messages per second vs. SpamAssassin’s tens or a whole lot), Bayesian filtering, and a cleaner configuration mannequin. For brand new deployments in 2026, Rspamd is the higher alternative.
Rspamd integrates with Postfix through the milter interface. Configure it to reject messages scoring above 15 (clear spam), quarantine messages scoring 6-15 (possible spam), and go messages under 6. Tune these thresholds based mostly in your first month’s false optimistic price.
DNS Blocklists and Actual-Time Checks
- DNSBL checks: Configure Postfix to reject mail from IPs listed on Spamhaus, Barracuda, and comparable blocklists on the SMTP connection degree. This stops spam earlier than Rspamd has to guage it.
- Greylisting: Briefly reject mail from unknown senders; reputable mail servers retry, spam bots usually don’t. Postgrey or Rspamd’s greylisting module handles this.
- Fee limiting: Postfix’s anvil daemon tracks connection charges per sending IP. Limiting connections per minute per IP stops burst-sending from compromised accounts.
Storage Planning for Mailboxes
Capability Calculation
Mailbox storage necessities rely closely on retention insurance policies and person habits. A practical planning system: common mailbox dimension x variety of mailboxes x retention issue.
| Mailbox Depend | Avg Dimension | 2-Yr Retention | Advisable Storage |
| 50 mailboxes | 5GB every | 500GB | Important (1.92TB NVMe) |
| 200 mailboxes | 10GB every | 4TB | Superior + exterior backup |
| 500 mailboxes | 10GB every | 10TB | A number of servers or NAS attachment |
| 1,000 mailboxes | 10GB every | 20TB | Devoted storage infrastructure |
Dovecot’s maildir format shops every message as a separate file. On NVMe storage, IMAP folder itemizing and search operations that may be sluggish on spinning disk full rapidly even for giant mailboxes with tens of 1000’s of messages. Customers on Dovecot-backed IMAP with NVMe storage discover sooner folder switching and search vs. hosted e mail companies that provision shared storage.
Dovecot Full-Textual content Search
Dovecot’s FTS (Full Textual content Search) plugin indexes mailbox contents for quick server-side IMAP SEARCH operations. With out it, IMAP search scans each message file sequentially. With it, search queries towards a 50GB mailbox full in milliseconds. Solr or Flatcurve (Dovecot’s newer built-in FTS backend) present this functionality. FTS indexes require roughly 15-20% extra storage overhead relative to mailbox dimension.
Microsoft Change on Devoted Home windows Servers
Change Server requires Home windows Server licensing and considerably greater {hardware} necessities than a Linux mail stack. Change 2019 minimal specs are 128GB RAM for the Mailbox position, although manufacturing deployments ought to plan for extra. This aligns properly with InMotion’s Excessive Devoted Server at 192GB DDR5 ECC RAM.
Change licensing (or Microsoft 365 E3/E5 for hosted Change) provides substantial value on prime of server infrastructure. For organizations standardized on the Microsoft ecosystem with Outlook purchasers, Groups integration necessities, or Unified Messaging wants, Change on devoted {hardware} stays the fitting alternative. For organizations evaluating recent, a Linux mail stack with Roundcube or SOGo webmail is considerably decrease value.
Compliance Logging Necessities
HIPAA E mail Compliance
HIPAA requires that e mail containing Protected Well being Info (PHI) be encrypted in transit (TLS) and at relaxation, with entry logs demonstrating who accessed which messages. Postfix enforces opportunistic TLS on outbound mail; configure necessary TLS with certificates verification for recognized healthcare accomplice domains. Dovecot logs all IMAP connections and folder entry occasions.
SEC 17a-4 and Authorized Maintain
Monetary companies corporations topic to SEC Rule 17a-4 should retain enterprise communications for 3-7 years in a non-rewritable, non-erasable format. Self-hosted e mail with write-once storage (or a compliance journal configured to repeat all mail to an immutable archive) satisfies this requirement. Third-party archiving instruments like MailStore Server combine with Postfix/Dovecot to supply compliant archiving.
Authorized Maintain for Litigation
When litigation locations e mail on authorized maintain, the power to protect and produce particular mailboxes or date ranges is important. Self-hosted e mail with direct filesystem entry makes this easy: protect the maildir directories, export through a forensically sound course of, and supply chain-of-custody documentation. Hosted e mail companies add lawyer and discovery charges to this course of that devoted internet hosting eliminates.
Server Configuration Suggestions by Scale
- Beneath 100 mailboxes (Important): Postfix + Dovecot + Rspamd suits comfortably with 64GB RAM. IMAP index cache makes use of 4-8GB. Storage ample for 5-year retention at common mailbox sizes.
- 100-500 mailboxes (Superior): Identical stack; extra RAM headroom for FTS index and Dovecot connection dealing with beneath greater concurrent person load.
- Change Server (Excessive): 192GB DDR5 ECC meets Change 2019 manufacturing necessities. ECC RAM prevents bit-flip corruption in Change database information.
Getting Began
InMotion’s APS workforce can help with Postfix and Dovecot preliminary configuration beneath Premier Care. For organizations migrating from hosted e mail to self-hosted, InMotion Options handles the mailbox migration course of, which is usually probably the most time-sensitive a part of the transition.
