DO
Make the change safely.
Practical procedures for the work: publish records, test authentication, diagnose delivery problems and operate email without guessing.
Add IPv6 to a mail server
Publish IPv6 only after SMTP, firewall, reverse DNS and authentication are ready.
Analyze a DMARC aggregate report
Turn a DMARC XML report into an actionable sender inventory check.
Analyze an email delivery delay
Use Received timestamps and queue logs to find where the time was actually spent.
Analyze an email header
Step-by-step guide to tracing email delivery hops, authentication results, delays and suspicious sender identities.
Audit a DMARC deployment
Review policy, alignment, reporting and subdomain behavior as one system.
Audit an SMTP relay
Review authorization, TLS, logging and abuse controls on application relay infrastructure.
Audit an SPF policy
Map every mechanism to a real sender and remove authorization that no longer has a purpose.
Audit DKIM selectors
Find active, stale and unknown DKIM keys without deleting evidence blindly.
Audit Exchange Online connectors
Find stale partner, gateway and application routing dependencies.
Audit Google Workspace mail routing
Document default routing, split delivery, gateways and recipient changes before troubleshooting loops.
Audit mailbox forwarding
Find intentional and suspicious forwarding before it becomes invisible data movement.
Audit organizational email domains
Build a domain inventory before authentication and routing become tribal knowledge.
Audit SMTP AUTH use in Exchange Online
Find applications and accounts still using authenticated SMTP before tightening policy.
Build a postmaster runbook
Give operations a repeatable first response for delayed, rejected and suspicious mail.
Build a useful mail-flow diagram
Document systems and trust boundaries so troubleshooting does not start from guesswork.
Bulk sender readiness checklist
Prepare authentication, DNS, unsubscribe and list operations before increasing volume.
Change a DMARC report destination
Move aggregate reporting without creating a blind spot.
Change email DNS safely
Use authoritative verification, staged TTLs and post-change message tests.
Change SPF during a sender migration
Authorize overlapping legitimate sources without creating multiple SPF policies.
Check a domain's email DNS
A repeatable workflow for MX, SPF, DKIM, DMARC and transport-policy checks.
Check an SMTP TLS certificate
Verify the certificate presented by the actual mail endpoint, not a website with the same domain.
Check reverse DNS for an outbound mail server
Verify PTR and forward DNS without confusing rDNS with authentication.
Configure DKIM
Publish a selector and verify production signing end to end.
Create a deliverability baseline
Know normal authentication, bounces and complaint behavior before an incident.
Create an email sender inventory
Find every platform that uses your domains before changing authentication.
Decommission a SaaS email sender
Remove the vendor from mail flow, DNS and credentials instead of merely canceling the subscription.
Decommission an email sending service
Remove a former sender without breaking other mail paths.
Deploy DMARC safely
Move from visibility to enforcement without blocking legitimate senders.
Deploy MTA-STS and TLS-RPT
Add SMTP transport policy and reporting with a staged rollout.
Design an application email sender
Choose identity, authentication, retry and telemetry before writing the send-email call.
DMARC fails even though DKIM passes
A valid signature from the wrong domain does not satisfy DMARC alignment.
DMARC fails even though SPF passes
Check alignment before assuming the receiver evaluated DMARC incorrectly.
Email DNS migration runbook
Change MX and authentication records without treating DNS as a single cutover switch.
Email infrastructure monitoring checklist
Monitor the dependencies that can break mail even while the SMTP process is still running.
Email security gateway migration checklist
Move between gateways without losing routing, authentication, DLP or visibility.
Email service recovery runbook
Restore mail in dependency order and use SMTP retry behavior to your advantage.
Google Workspace mail flow checklist
Review routing, gateways, SMTP relay and authentication around Google Workspace.
Google Workspace SMTP relay planning
Plan application relay around allowed senders, source authorization and current Workspace settings.
Hunt a malicious attachment across email
Use hashes and message metadata to scope attachment-based campaigns.
Hunt a malicious URL across email
Pivot from one reported message to the rest of the campaign.
Implement one-click unsubscribe
Add RFC 8058 unsubscribe behavior without turning a preferences page into fake one-click support.
Introduce a new sending domain or IP
Operational considerations for establishing a new outbound sending identity.
Investigate a 550 5.7.1 rejection
A practical workflow for one of the most common but least specific SMTP errors.
Investigate a compromised mailbox
Scope identity, mailbox persistence and malicious mail activity together.
Investigate a quarantined message in Microsoft 365
Use the detection reason and message evidence before releasing mail.
Investigate a spam-complaint spike
Find the campaign or acquisition problem before reputation damage spreads.
Investigate a suspected phishing email
A header-first workflow that preserves evidence and separates spoofing from account compromise.
Investigate SMTP 421 responses
Treat 421 as a service-level temporary failure and preserve the provider's diagnostic text.
Investigate SMTP 451 responses
Work a temporary local-processing failure without suppressing a valid recipient.
Investigate SMTP 554 responses
Use the enhanced code and diagnostic text because 554 alone is not a root cause.
Investigate SPF permerror
Treat a permanent SPF evaluation error as a broken policy, not a neutral result.
Lab: analyze a message header
Practice separating transport, authentication and visible message identities.
Lab: read an SMTP session
Learn the transaction without using somebody else's server as a relay test.
Lab: trace email DNS by hand
Walk from a domain to its MX, addresses, SPF, DMARC and DKIM records.
Mail queue incident runbook
Use age, destination and response patterns to decide whether a queue is healthy backlog or an outage.
Microsoft 365 application and device sending
Choose among authenticated submission, SMTP relay and direct-send style paths based on the requirement.
Microsoft 365 mail flow checklist
Review the major mail-flow and authentication pieces around Exchange Online.
Migrate DKIM between email providers
Use selectors to overlap old and new signing rather than forcing a flag-day key replacement.
Monitor an SMTP queue
Turn queue depth and age into useful operational signals.
Monitor email authentication drift
Catch new senders and broken alignment before users report deliverability problems.
Monitor email infrastructure
What to monitor across DNS, SMTP, TLS, queues and authentication.
Move DMARC toward reject
Use reporting and sender inventory to reach enforcement without breaking legitimate mail.
Plan an email platform migration
Reduce delivery and authentication failures during a mail-platform change.
Plan MX redundancy
Add secondary mail exchangers only when they are equally secured and operationally understood.
Prepare a domain for bulk sending
Technical readiness before a new organization begins high-volume email.
Preserve evidence during an email incident
What to retain before messages, logs and cloud telemetry disappear.
Prevent email loops
Design automated responders and forwarding rules to avoid runaway mail.
Process unsubscribes safely
Make suppression durable across campaigns and avoid accidentally resubscribing people.
Publish a DMARC record
Deploy DMARC deliberately, collect reporting data and progress toward enforcement without breaking legitimate senders.
Publish an SPF record
Build SPF from an inventory of legitimate outbound senders.
Renew a mail TLS certificate
Replace certificates on every real SMTP/IMAP/submission endpoint and verify what clients actually receive.
Respond to a compromised mailbox
Contain account takeover and investigate malicious email sent from a legitimate account.
Respond to an email blocklist listing
Stop the behavior first, identify the exact list, then follow its remediation process.
Respond to an email blocklist listing
Fix the cause before requesting reputation delisting.
Respond to outbound spam from your environment
Contain the sending identity first, then repair reputation and configuration.
Respond to suspected business email compromise
Contain the account and business process, not just the malicious message.
Retire an email domain safely
Stop receiving and sending without leaving stale authentication and forgotten mail paths behind.
Review Exchange Online accepted domains
Know whether each domain is authoritative or participates in another routing design.
Review Microsoft 365 anti-phishing configuration
Check impersonation and spoof protections as part of the broader mail-security posture.
Review SMTP logs efficiently
Use identifiers and transaction boundaries instead of searching giant logs by subject line.
Roll out an email DLP policy
Start with evidence and tuning before turning a broad detector into a production block.
Rotate an SMTP application credential
Change application mail credentials without creating an avoidable outage.
Rotate DKIM keys
Rotate selectors without breaking validation for in-flight mail.
Secure an email event webhook
Treat delivery callbacks as untrusted Internet requests until verified.
Secure an SMTP relay
Prevent open relay while supporting applications and trusted senders.
Secure partner mail flow in Exchange Online
Use connectors deliberately when a partner path needs stronger transport or source restrictions.
Secure postmaster, abuse and other role mailboxes
Keep operational addresses reachable without turning them into forgotten shared credentials.
Self-hosted mail readiness checklist
A preflight before exposing your own mail server to the Internet.
Separate transactional and marketing mail
Design sending identities so one traffic class does not dominate another.
Separate transactional and promotional mail
Reduce operational coupling between critical notifications and higher-risk subscription traffic.
Set up bounce processing
Classify delivery failures and suppress addresses appropriately.
Test an email disaster-recovery plan
Exercise mail dependencies without learning the plan is theoretical during a real outage.
Test an SMTP service safely
Validate connectivity, capabilities and relay policy without sending arbitrary mail.
Test an SMTP submission service
Validate EHLO, TLS and authentication without treating submission like an open-relay test.
Test authentication through a mailing list
See exactly which authentication mechanisms survive redistribution.
Test MX failover
Verify backup mail paths without creating a production outage.
Test relay controls safely
Verify your own SMTP server cannot relay arbitrary third-party mail.
Test SPF DKIM and DMARC
Validate real production authentication from received message evidence.
Trace a delayed message
Use Received headers and server logs to find where time was actually lost.
Trace a message in Exchange Online
Use Microsoft 365 message trace to determine what Exchange Online did with a message.
Troubleshoot 5.1.1 recipient failures
Verify the address and directory before blaming sender reputation.
Troubleshoot 5.7.1 policy rejections
Use the receiver's diagnostic to distinguish relay, authentication, reputation and content policy.
Troubleshoot an email loop
Find the repeated hop or automation instead of deleting copies one mailbox at a time.
Troubleshoot delayed email
Find where a message waited by correlating headers, queues and SMTP responses.
Troubleshoot DKIM failures
Diagnose selector, DNS, signing and message-modification problems.
Troubleshoot DKIM that fails after a gateway
Compare the message before and after the intermediary instead of rotating keys blindly.
Troubleshoot DMARC failures
Determine why an authenticated message still fails DMARC.
Troubleshoot DNSSEC-related email failures
Recognize when signed DNS is failing validation rather than simply returning no record.
Troubleshoot email bounces
Use SMTP and DSN evidence to identify the actual failure class.
Troubleshoot message-too-large failures
Account for MIME expansion and every hop's size limit.
Troubleshoot missing email webhook events
Separate provider delivery from callback-delivery failures.
Troubleshoot missing or broken MX records
Determine whether mail routing is failing at DNS before investigating the mailbox platform.
Troubleshoot missing TLS-RPT reports
Verify policy publication and remember that reporting depends on participating senders.
Troubleshoot MTA-STS
Check the DNS signal, HTTPS policy, MX patterns and certificates as separate dependencies.
Troubleshoot reverse DNS for a sending IP
Verify the PTR at the IP owner and the corresponding forward address record.
Troubleshoot SMTP timeouts
Find the exact transaction phase that stalled before blaming the network.
Troubleshoot SMTP TLS
Diagnose STARTTLS, certificates, protocol compatibility and policy failures.
Troubleshoot spam placement
Investigate accepted messages that land in junk.
Troubleshoot SPF failures
Trace the evaluated domain, source IP and DNS mechanisms behind an SPF result.
Use Google Workspace Email Log Search
Trace Workspace handling before assuming a message vanished.
Validate a bulk email before launch
Check a real rendered message and its transport metadata before sending at scale.
Validate an email DNS change
Prove a DNS change is authoritative before blaming propagation.
Verify an email platform cutover
Prove inbound, outbound, application and authentication paths after migration.
Work safely with Exchange Online mail flow rules
Avoid broad transport-rule changes that unexpectedly rewrite, redirect or reject production mail.