Pronunciation of 'je suis à'

Question

Is it right that you don't pronounce the 'S' at the end of 'suis' when it's followed by 'à'?

I had thought anytime a vowel sound follows a word ending in 's', you pronounce that s. Like with 'Je dine dans une...'

Accepted Answer

A limited number of liaisons are 'required', some are 'forbidden', and some are optional. 
This one is optional - optional liaisons are less frequently used in modern everyday French than previously, and can sound quite formal. This would be one of the more formal ones to use.
See links: 
https://www.lawlessfrench.com/pronunciation/optional-liaisons/ https://www.lawlessfrench.com/pronunciation/required-liaisons/ https://www.lawlessfrench.com/pronunciation/forbidden-liaisons/