What would you call 'A person who is ready for support all the time'

What would you call 'A person who is ready for support all the time'?

I wanted to write an email and convey to some clients that I will always be there for support, and was stuck when I got to this.

Solution 1:

Not sure if that's exactly what you were looking for, but I would write something like

Please do not hesitate to contact me again if you require further assistance.

Solution 2:

Though the term is rather casual, a "go-to guy" (or "go-to person") is someone who is continuously available for help and support in a professional environment.

Solution 3:

A generally acceptable phrase for this is on-call.

I am available on-call.

My contract includes 24/7 on-call technical support.

I may have to leave early if my phone rings because I'm on-call.