Outgoing email breaks when the site moves host

Why this page exists

Last checked: 11 August 2026.

Moving the website to a new host does not move the website's outgoing email settings. Those live inside WordPress, they keep pointing at the old host, and when the old host finally stops accepting the login every form on the site goes silent without warning. This has already happened once. Read this before and after any hosting change.

What happened in 2026

Between 29 July and 10 August 2026 the website sent no form notification emails at all. Twelve days, roughly 55 submissions, nobody told about any of them: newcomer pack SMS requests, new meeting registrations, meeting detail updates and broken meeting link reports.

The forms themselves worked the whole time. Every submission was saved correctly in WPForms. Only the notification email failed.

Cause

The site moved from SiteGround to Krystal, but WP Mail SMTP was left pointing at SiteGround:

SiteGround carried on accepting the login for a while after the move, so nothing looked wrong. On 29 July it stopped, and from then on every send failed with SMTP Error: Could not authenticate.

Why it went unnoticed for twelve days

Worth understanding, because the same blind spots are still there:

• WPForms saves the entry first and emails second. A failed email leaves no visible trace on the website.
• An SMTP authentication failure produces no bounce message. Nothing arrives anywhere, so no mailbox shows an error.
• WP Mail SMTP Lite has no failed-email alerts. That is a Pro feature.
• To anyone using the site, the forms looked completely normal.

The only symptom was an absence: two mailboxes that normally receive several emails a day receiving nothing.

Checklist for the next hosting move

1. Create the sending mailbox on the new host first. WP Mail SMTP authenticates as a real mailbox. It must exist on the new host before you change anything.
2. Check what From address the new host will accept. Some hosts only allow a From address that exactly matches the mailbox you authenticate as. LCN is one of these and rejects anything else with a 554, including other addresses on the same domain. Krystal is more relaxed. If the new host is strict, set From Email to the authenticating mailbox and turn on Force From Email.
3. Update WP Mail SMTP on every site in the network that has it active. This is a WordPress Multisite. Plugin activation is per site, so check each one. As of August 2026 only forms.cocaineanonymous.org.uk has it active.
4. Update SPF in Cloudflare DNS. Add the new host. Check the hostname you reference actually resolves to the origin server and not a Cloudflare proxy IP, which means it must be set to DNS only (grey cloud), not Proxied.
5. Update DKIM in Cloudflare DNS. The default._domainkey record holds the public key of whichever host signs the mail. The new host generates its own key, usually under cPanel > Email Deliverability. Leaving the old key in place fails DKIM silently.
6. Send a test. WP Mail SMTP > Tools > Email Test.
7. Confirm it arrived and check the headers. Look for spf=pass and dkim=pass in the Authentication-Results header. Delivery on its own is not proof: mail that fails SPF or DKIM often still gets through, until one day it goes to spam instead.

Current configuration

As at 11 August 2026, after the fix.

Use mail.cocaineanonymous.org.uk as the SMTP host rather than the IP address or p156.lon.krystal.io. The TLS certificate on the Krystal mail server is valid for that name, and covers the site subdomains too. The bare Krystal hostname has a different certificate and an IP address will not verify at all.

Still to do

• Incoming mail for cocaineanonymous.org.uk still routes to SiteGround. The MX records point at mailspamprotection.com, which is SiteGround's filtering. Before changing them, list every mailbox and forwarder still held there and recreate them on Krystal, otherwise incoming mail will start bouncing. Once the MX records point at Krystal, the +mx term in SPF covers it automatically and the two SiteGround terms can be removed.
• DMARC rua and ruf both point at admin@cocaineanonymous.org.uk, so DMARC reports are going to SiteGround.
• WP Mail Logging is installed on the forms site but inactive. Turning it on gives a log of every send and every failure, which is the free substitute for the Pro alerts.

How to spot this happening again

Form notifications normally arrive most days. If wtf@cauk.org.uk or itcommittee@cauk.org.uk goes quiet for more than about two days, assume the mailer has broken rather than that submissions have stopped.

To confirm, open WPForms > Entries on forms.cocaineanonymous.org.uk. If entries are still arriving but no emails are, the fault is the mailer, not the forms. Then check WP Mail SMTP > Tools > Email Test for the actual error.