How to distinguish the below letters clearly when talking with someone on the phone?

I found a little trouble when I talking with some clients on the phone, especially when we offer emails to each other. You know, there might be some pronunciation differences between each other, and this makes us a little confused when we spell emails.
The letters like g-j, m-n, c-z, although I spell very clearly, but the listener still can not find the correct one, or the speaker sometimes makes me confused when he offers email to me. So, is there anygood way to distinguish the above letters in a mail or other words?
Well, this takes so much time when we talking business on phone, sometimes it consists half of the conversation.
Waiting for some quick respond

Hi cajndon,

What I used to do when working in a customer service area was to always follow the letter with an “as in…”. For example: “G as in Greenland”, “J as in Jamaica”, etc… This was there was no room for confusion.

If your customer is the one spelling, you can always reply back with a question using the same technique: “G as in Greenland?- Ok!”

I hope this helps you and makes your life easier. I know how bad customers can get!

And can anybody tell me how to say some normal symbols like _,- in an email? Thank you in advance!

Hi cajndon, again coming from my customer service experience, I think these are the most important ones you will probably have to use:

@ - at
/ - slash
_ - underscore

    • hyphen
      , - comma
      . - dot

Thank you Falcao, I learned a lot.