chasquid doesn't directly request the certificates, so you'd have to use
your serverless service's API to get them.
Note that, in any case, most serverless services will not allow you to
send emails anyway, they block outgoing connections to port 25.
For an email server like chasquid, it is much more practical (and often
cheaper!) to use a small VPS rather than running them in a serverless
environment.
I hope this helps!
Thanks!
Alberto