Subscription form times out with no confirmation email
I've just installed Sendy for the first time (latest, 6.0.9) and have Sendy configured so that it can send emails correctly. I'm now trying to create a page on my website that includes the Subscription Form that I got by following the FAQ instructions.
When I use the subscription form, the name and email I entered are added to the subscriber list in Sendy, however I do not receive a confirmation email (I have double opt-in set), and if I leave the page open for a while I get a 524 error for the /sendy/subscribe page (which is where the POST request is sent, if I understand correctly).
If I try again with the same email address, I'm almost immediately sent to the /sendy/subscribe page and the "a confirmation email had already been sent to you" message is displayed.
Please advise on what to check so I can fix this.