My grandparents married in Sarreguemines Synagogue in France in 1927.
Under French civil law at that time, were they also required to have a civil marriage?
If yes, then I believe that happened in Strasbourg.
Can I please receive advice on how to obtain a copy of their civil marriage record (email, post??)
They were required to have a civil marriage. You can search
here for Sarreguemines
here for Strasbourg
Decennial tables (in alphabetic order), will give you the date. When you have the date, you can ask a full copy at the city Hall
Sarreguemines : https://www.sarreguemines.fr/page/32-actes-detat-civil
Strasbourg : https://www.strasbourg.eu/contact-service-etat-civil