Email Security Guides
SPF
- How do ip4 and ip6 mechanisms work in SPF?
- Setting up SPF at All-Inkl
- Setting up SPF at Amazon Route 53
- Setting up SPF at checkdomain
- Setting up SPF at Cloudflare
- Setting up SPF at dogado
- Setting up SPF at domainfactory
- Setting up SPF at Gandi
- Setting up SPF at GoDaddy
- Setting up SPF at Hetzner DNS
- Setting up SPF at Hostinger
- Setting up SPF at IONOS
- Setting up SPF at Netcup
- Setting up SPF at one.com
- Setting up SPF at OVHcloud
- Setting up SPF at Strato
- Setting up SPF at united-domains
- Setting up SPF at webgo
- Setting up SPF for Google Workspace
- Setting up SPF for Mailcow (self-hosted)
- Setting up SPF for Microsoft 365
- What do -all, ~all, ?all, and +all mean in SPF?
- What do the a and mx mechanisms check in SPF?
- What does the exists mechanism do in SPF?
- What does the include mechanism do in SPF?
- What does the redirect modifier do in SPF?
- Why should you avoid the ptr mechanism in SPF?
DKIM
- Setting up DKIM at All-Inkl
- Setting up DKIM at Amazon Route 53
- Setting up DKIM at checkdomain
- Setting up DKIM at Cloudflare
- Setting up DKIM at dogado
- Setting up DKIM at domainfactory
- Setting up DKIM at Gandi
- Setting up DKIM at GoDaddy
- Setting up DKIM at Hetzner
- Setting up DKIM at Hostinger
- Setting up DKIM at IONOS
- Setting up DKIM at Netcup
- Setting up DKIM at one.com
- Setting up DKIM at OVHcloud
- Setting up DKIM at Strato
- Setting up DKIM at united-domains
- Setting up DKIM at webgo
- Setting up DKIM for Google Workspace
- Setting up DKIM for Mailcow (self-hosted)
- Setting up DKIM for Microsoft 365
- What is a DKIM selector and what is it used for?
- What is Ed25519 in DKIM and why is it superior to RSA?
- What is the structure of a DKIM DNS record?
- Which key length is best for DKIM: 1024 or 2048 bits?
DMARC
- Setting up DMARC at All-Inkl
- Setting up DMARC at Amazon Route 53
- Setting up DMARC at checkdomain
- Setting up DMARC at Cloudflare
- Setting up DMARC at dogado
- Setting up DMARC at domainfactory
- Setting up DMARC at Gandi
- Setting up DMARC at GoDaddy
- Setting up DMARC at Hetzner
- Setting up DMARC at Hostinger
- Setting up DMARC at IONOS
- Setting up DMARC at Netcup
- Setting up DMARC at one.com
- Setting up DMARC at OVHcloud
- Setting up DMARC at Strato
- Setting up DMARC at united-domains
- Setting up DMARC at webgo
- Setting up DMARC for Google Workspace
- Setting up DMARC for Mailcow (self-hosted)
- Setting up DMARC for Microsoft 365
- What do adkim= and aspf= mean in DMARC? (Relaxed vs Strict)
- What do p=none, p=quarantine, and p=reject mean in DMARC?
- What does the pct= tag do in DMARC and how does it aid rollout?
- What does the sp= tag do in DMARC and when do you need it?
- What is the difference between rua= and ruf= in DMARC?
- What is the fo= tag in DMARC and what options are available?
DANE & DNSSEC
MTA-STS
TLS-RPT
BIMI
Blocklists (DNSBL)
Port 25 Blocks
- AWS (Amazon EC2) Port 25 Block: Unblocking Policy and Alternatives
- Contabo Port 25 and Email Sending Policy: Rate Limits and Reputation
- DigitalOcean Port 25, 465, and 587 Block: Why SMTP is Restricted on Droplets
- Google Cloud (Compute Engine) Port 25 Block: Policy and Alternatives
- Hetzner Cloud Port 25 Block: Unblocking, Policy, and Alternatives
- IONOS Port 25 Block: Unblocking Requirements, Policy, and Alternatives
- Microsoft Azure Port 25 Block: Subscription Rules and Alternatives
- netcup Port 25 Block (Mail block policy): Removal, Rules, and Alternatives
- Oracle Cloud (OCI) Port 25 Block: June 2021 Cutoff and Exemption Requests
- OVHcloud Port 25 Block: Support Unblocking Policy and Alternatives
- Scaleway Port 25, 465, and 587 Block: KYC Unblocking and Security Groups
- STRATO Server Port 25 Block: Unblocking and Alternatives
- Vultr Port 25 Block: Support Ticket Unblocking and Alternatives
SMTP Error Codes
- Gmail SMTP Errors 550 5.7.26, 421 4.7.28 & 4.7.25: Meaning and Fixes
- GMX & WEB.DE SMTP Error 554 IP Address is Block Listed & 421 Retries
- IONOS SMTP Error 550 Reject due to policy restrictions & HELO Throttling
- Outlook SMTP Error 5.7.606: Banned Sending IP and Custom Block Lists
- T-Online SMTP Error 554 IP Blocked: Causes and Delisting via tosa@rx.t-online.de
- Yahoo SMTP Errors 421, 451, 553 & 554: Meaning and Solutions
Other
- Choose your provider: email-security setup guides by host
- Configure SPF and DMARC in Plesk
- Disable Outdated TLS Versions and Weak Ciphers in Exim
- DNSBL Blocklist Directory: Check, Delisting, and Verdicts
- Enable and Configure DKIM in Plesk
- Enable and Configure STARTTLS in Exim
- Enable and Configure STARTTLS in Sendmail
- Enable and Enforce STARTTLS in Postfix
- How to Disable Legacy TLS Versions and Weak Ciphers in Postfix
- Manage Email Deliverability in cPanel
- Outbound Port 25 Block by Cloud Provider: Overview and Unblocking
- rspamd 4.1.2 fixes remote DoS in the MIME parser
- rspamd 4.1.3 fixes out-of-bounds read in DKIM signature verification
- rspamd 4.1.4 fixes critical authentication bypass in the controller
- Set Up DKIM Signing in Rspamd
- Set Up DKIM Signing with OpenDKIM
- SMTP Error Dictionary: Common Bounce Codes by Provider
- SPF vs DKIM vs DMARC: how they fit together
- SPF, DKIM & DMARC provider comparison: Overview of all 27 hosts
- TLS 1.2 is frozen: IETF deprecates RSA and FFDHE key exchange
- What is email authentication? SPF, DKIM, DMARC and the transport layer
- Which provider supports DANE and MTA-STS? Overview of all 27 hosts