You should have replied to his letter.

We look forward to receiving your quote by return mail.

If you cannot join us, please reply.

Finally, I have time to reply to the mail that I have received these past three weeks.

Please write me a reply soon.

Please send me a reply as soon as you receive this mail.

I'm sorry I'm late replying to your email.

You can't just answer emails from people you don't know.

We will put this matter on hold until he replies tomorrow.

Please send me a reply as soon as you receive this mail.

As soon as you see this e-mail, please reply right away.

This e-mail address is only able to send emails. Even if you reply to this email, we cannot respond, thanks in advance for your understanding.

You don't have to answer if you don't want to.

Looks like everyone can reply in English so quickly. Ah, or maybe I'm just too slow.

Sorry to be slow replying.

I didn't notice your reply, sorry.

Thank you for your prompt reply.

Include a stamped addressed envelope if you want a response.

Tom didn't text Mary back.