Hi @Merlin, the most common issue with contact form email delivery is the “From” email address being incorrectly set. Sitely defaults to noreply@example.com, which used to work 10 years ago, but with the tightening spam checking is no longer good in many cases.
A not very well known fact of email on the internet is that 99% of the email is spam, and does not make it to any mailbox (including the spam/junk email folder), it just gets outright deleted. There are dedicated network appliances that do this (Cisco Ironport, Barracuda). If the rating for the email is below a certain threshold it gets accepted to some folder and delivered, including spam if it still doesn’t look great.
Now one way to detect if email is spam that has been increasingly applied across most mail services, and all big mail services (gmail, yahoo, icloud, hotmail), is to check the domain’s SPF record (Sender Policy Framework). The SPF record is attached to the domain, in the DNS, and lists the servers that are allowed to send email for the domain. This record is checked for the sender, so the “from” in the Sitely settings.
The default example.com domain has a restrictive SPF records that states that no server is allowed to send email on behalf of the example.com domain, so logically any email with that from address reaching a recipient email server that checks SPF will be deleted.
If you want too share a screenshot of the send button settings we can take a look.