--- title: Guides url: 'https://omnivery.com/resources/guides' markdown: 'https://omnivery.com/resources/guides.md' lang: en date: '2026-09-06' description: 'SPF, DKIM and DMARC, bounce codes, SMTP ports, relay setup for Microsoft 365 and Google Workspace, IP warming, dedicated vs shared IPs, and the rules behind unsubscribes.' --- Resources # Email infrastructure guides Our guides cover four critical areas of email infrastructure: platform and protocol configuration, including documented limits; standards, compliance, and consent requirements that govern what you can send and measure; infrastructure decisions that determine how email is sent and delivered; and failure analysis to help you understand what happened when a message doesn't reach its destination. Every guide is grounded in primary sources from the platform provider, regulator, or standards body itself. ## Available guides ### Office 365 SMTP relay setup The four ways to send application email through Microsoft 365, what each one actually allows, and the limits Microsoft documents for them. Read the guide[Office 365 SMTP relay setup](https://omnivery.com/resources/guides/office-365-smtp-relay) ### Google Workspace SMTP relay setup The difference between the SMTP relay service, Gmail SMTP and restricted Gmail, with Google's documented limits for each. Read the guide[Google Workspace SMTP relay setup](https://omnivery.com/resources/guides/google-workspace-smtp-relay) ### The List-Unsubscribe header What the header does, how RFC 8058 one-click unsubscribe works, and exactly what Google, Yahoo and Microsoft each require of bulk senders. Read the guide[The List-Unsubscribe header](https://omnivery.com/resources/guides/list-unsubscribe-header) ### Double opt-in, and how bots break it What double opt-in is, what GDPR actually requires, and why automated security scanners confirm subscriptions nobody agreed to. Read the guide[Double opt-in, and how bots break it](https://omnivery.com/resources/guides/double-opt-in) ### The email pixel consent map Which tracking-pixel purposes need consent under the EDPB guidelines and the CNIL recommendation, and the narrow deliverability lane that does not. Read the guide[The email pixel consent map](https://omnivery.com/resources/guides/tracking-pixel-consent) ### IP and domain warming How warming works, why domain reputation now matters more than IP reputation, and why automated rate limits beat a manual schedule. Read the guide[IP and domain warming](https://omnivery.com/resources/guides/ip-and-domain-warming) ### Dedicated vs shared IP Why a dedicated IP fails for senders with spiky volume, how a shared pool stays warm, and the test that decides which one you need. Read the guide[Dedicated vs shared IP](https://omnivery.com/resources/guides/dedicated-vs-shared-ip) ### SMTP ports explained What ports 25, 465, 587 and 2525 are each for, why outbound 25 is blocked almost everywhere, and which one to configure. Read the guide[SMTP ports explained](https://omnivery.com/resources/guides/smtp-ports) ### Email bounces explained Hard versus soft bounces, how to read an SMTP bounce code, why the code is sometimes wrong, and what to do about the bounces nobody can parse. Read the guide[Email bounces explained](https://omnivery.com/resources/guides/email-bounces) ### SPF, DKIM and DMARC explained How the four authentication standards fit together, why alignment matters more than any single record, what DMARCbis changed in 2026, and where DKIM2 actually stands. Read the guide[SPF, DKIM and DMARC explained](https://omnivery.com/resources/guides/email-authentication) ### BIMI: the record, the logo and the certificate What BIMI is and is not, the DMARC policy it requires before any logo appears, the record and SVG format, VMCs versus CMCs, and which mailbox providers actually show the logo. Read the guide[BIMI: the record, the logo and the certificate](https://omnivery.com/resources/guides/bimi) ## Need the API reference instead? The full developer documentation, including every SMTP header and API endpoint, lives at omnivery.com/docs. [Read the documentation](https://omnivery.com/docs)[See the SMTP relay](https://omnivery.com/products/smtp-relay) --- ## Navigation - Parent: [Resources](https://omnivery.com/resources.md) - Previous: [Case Studies](https://omnivery.com/resources/case-studies.md) - Next: [Non-Human Interactions](https://omnivery.com/resources/non-human-interactions.md) - Children: - [BIMI](https://omnivery.com/resources/guides/bimi.md) - [Email Authentication](https://omnivery.com/resources/guides/email-authentication.md) - [Email Bounces](https://omnivery.com/resources/guides/email-bounces.md) - [SMTP Ports](https://omnivery.com/resources/guides/smtp-ports.md) - [Dedicated vs Shared IP](https://omnivery.com/resources/guides/dedicated-vs-shared-ip.md) - [IP and Domain Warming](https://omnivery.com/resources/guides/ip-and-domain-warming.md) - [Tracking Pixel Consent](https://omnivery.com/resources/guides/tracking-pixel-consent.md) - [Double Opt-In](https://omnivery.com/resources/guides/double-opt-in.md) - [List-Unsubscribe Header](https://omnivery.com/resources/guides/list-unsubscribe-header.md) - [Google Workspace SMTP Relay](https://omnivery.com/resources/guides/google-workspace-smtp-relay.md) - [Office 365 SMTP Relay](https://omnivery.com/resources/guides/office-365-smtp-relay.md)