Are these sentences appropriate?

[anupumh]

Hi,

Is there anything redundant or unnecessary in these sentences?

I will revert back to you on this.

Please reply back to my email.

You need to repeat again the sentence.

If you dont do this, you will lag behind others.

What should be the correct sentences?

Thanks

[Barb_D]

Hi,

Is there anything redundant or unnecessary in these sentences?

I will revert back to you on this.
I have learned that "revert" is Indian English, but before my time on ESL forums, I'd never encountered this usage. I will get back to you about this is what I would expect.

Please reply back to my email. No, just "please reply" with no "back."

You need to repeat again the sentence. Unless you already repeated them and need to do it again (for the third time or more) this is redundant.

If you don't do this, you will lag behind others. I don't find anything redundant here. I guess the dictionary says that "lag" as a transitive verb means "lags behind" but there are millions of hits for it, and The Free Dictionary lists "Lag behind."

What should be the correct sentences?

Thanks

...