So i've tried with both SES and mailgun as providers and no email gets sent. Theres no warning in console or in debug (except for Flarum\Http\Exception\RouteNotFoundException which is apparently not relevant). The only thing that seems odd is that the POST request for send-confirmation has no content:
Status Code: 204 No Content
Access-Control-Allow-Credentials
true
Access-Control-Allow-Headers
x-requested-with, Content-Type…-security-token, X-CSRF-Token
Access-Control-Allow-Methods
POST, GET, OPTIONS, DELETE, PUT
Access-Control-Allow-Origin
Access-Control-Expose-Headers
X-CSRF-Token
Access-Control-Max-Age
1000
Connection
Keep-Alive
Content-Type
text/html; charset=UTF-8
Date
Sat, 10 Mar 2018 14:03:33 GMT
Keep-Alive
timeout=5, max=97
Server
Apache/2.4.18 (Ubuntu)
Set-Cookie
flarum_session=3bkol023hbj6htg8f8bh1eelk4; Path=/; HttpOnly
X-CSRF-Token
snb6GRgPHiOYIC3ST6GD6Acvf3rP81PEc5tOalpG
Request headers (578 B)
Accept
/*
Accept-Encoding
gzip, deflate
Accept-Language
en-GB,en;q=0.5
Cache-Control
no-cache
Connection
keep-alive
Content-Length
0
Content-Type
text/plain;charset=UTF-8
Cookie
flarum_session=3bkol023hbj6htg…vSZu9y09Cp4P5uvYVeLMDx2BC32EF
Host http://x.com
Pragma
no-cache
Referer
http://x.com
User-Agent
Mozilla/5.0 (Windows NT 10.0; …) Gecko/20100101 Firefox/58.0
X-CSRF-Token
snb6GRgPHiOYIC3ST6GD6Acvf3rP81PEc5tOalpG
I've tried every combination of ports, tried SSL, TLS, starttls. I'm not sure where to look now