It appears that the sender address needs to be from the main domain (which it wasn’t) for this web hosting company and that flagged up the security issue as a potential spamming problem with an unknown email address. I’m hoping that I can use the bcc function to advise the organiser and use a no-reply@domain_name as the sender address in the future.
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This reply was modified 5 years, 6 months ago by peterbaldwin.
The problem appears to be with the hosting organisation as I found a message identifying that they had suspended some services due to their automated security system detecting unusual e-mail activity when I bulk emailed all 10 entries for an event last week. Due to having a bcc, it sent 20 emails out. Not sure why that was suspicious, but they have advised me that I can only get support between Monday to Friday, so will attempt to resolve tomorrow.
For info, PHP is Ver 7.4.10 and msqli is 5.7.30
