Email Provider that lets you use diffrent from addreesses


New Email
I run a small franchise (100 people) and I would like to send marketing emails on behalf of my clients, so I need the 'from' address to be their email, so if a prospect is interested, they contact the client and not me.

I only know one company that has this function, 'sendinblue' which quoted me £50k pa!
I have Googled it but cannot find any more companies.

Does anyone know of any other company that offers this function?

Thanks in advance.