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Knowledge Base & Operational DocumentationDomains, DNS & Business Email
Why Does Email Authentication Fail After Moving to a New Mail Provider?
Changing mail providers changes the systems authorized to send messages. Old SPF entries, missing DKIM keys, or a DMARC policy that expects the previous provider can cause messages to fail authentication even when users can send mail. What to check Identify all outbound senders, inspect message headers, and compare SPF, DKIM selector, and DMARC...
Why Does a Mail Server Reject Messages After Its IP Address Changes?
Changing an outbound mail IP can affect reverse DNS, SPF authorization, provider reputation, and recipient allowlists. Messages may be accepted by some domains and rejected by others. What to check Confirm the actual sending IP from message headers and compare PTR, forward DNS, SPF, DKIM, DMARC alignment, and rejection text. Check whether applications...
Why Does a Website Work on Desktop but Fail on a Mobile Network?
A mobile carrier or device may use different DNS, IPv6, proxy, or content filtering behavior than a home or office network. One network succeeding does not prove the domain resolves and serves correctly for all visitors. What to check Compare A and AAAA resolution, certificate and redirect behavior, proxy or CDN response, and network path across...
Why Does a New Domain Send Email but Not Receive It?
Outbound mail can work while inbound delivery fails if MX records are missing, point to the wrong host, or have not propagated. Some providers also require mailbox creation or domain verification before accepting messages. What to check Check authoritative MX and related host records, domain verification, mailbox existence, inbound gateway logs, and...
Why Does a Domain’s Website Work but Its Email Records Fail Validation?
Web and mail services can use different DNS records and providers. A site may load correctly while MX, SPF, DKIM, or DMARC records are missing, duplicated, or published in a zone that is not authoritative. What to check Query authoritative nameservers for mail records, confirm the exact hostname and TXT values, and compare with the active mail...
Why Does Email Delivery Stop After a Domain Name Is Renewed?
A renewal should preserve DNS, but expired nameservers, registrar lock changes, account ownership issues, or a missed DNS hosting renewal can interrupt mail even if the domain registration is current again. What to check Check registrar status, active nameserver delegation, authoritative MX records, DNS provider account, mail host availability, and...
Why Does a Website Work With IPv4 but Fail With IPv6?
A site can work over IPv4 while failing over IPv6 if an AAAA record points to the wrong host, the web server is not listening on IPv6, or firewall and certificate settings differ. Some visitors prefer IPv6 automatically. What to check Compare A and AAAA answers, test each route, inspect IPv6 firewall and listener configuration, and verify the hostname...
Why Does Email Work on Wi-Fi but Fail on a Mobile Network?
Email access can vary between Wi-Fi and mobile data because of VPN routing, DNS, firewall policy, carrier filtering, or mail app account configuration. The mailbox itself may be available while one network path is blocked. What to check Compare incoming and outgoing server names, ports and encryption, DNS answers, VPN state, carrier network behavior,...