Plugin slows down UX on web

Hi there,

Your plugin is great but… it breaks a UX level of the web.

This thread seems will continue that once from 2017.
That’s a pity but seems that since 2017 this “issue” was not solved.

Our booking system should send 3 emails after booking is done. So emails sent by wp_mail() just in 2-3 seconds after the booking complete.

Unfortunately sending the same emails via Post SMTP plugin gets 8…10 seconds (gets x3 times more time).
This is really dangerous because the customer can thing that is just hanging on the web and can go away. 🙁

We did try Google SMTP and Google API – there is no time difference.

We use the same booking system on 5 websites also as on dev versions of those webs (7 different hostings). So this is not a hosting issue for 100%.

Do you have any ideas?

The page I need help with: [log in to see the link]