I was told my amendment was prosses and will go out in the mail on the 26th af march does that mean I will receive it in the mail on the 26th of march or what does that mean?

If it is going in the mail on the 26th, then you will probably receive it within 1-2 weeks. They will never post the date that you will get it in the mail unless it's a direct deposit.

Yes it means that on that date ( more or less) it will be mailed. So depending on postal service, a few days to a week or so.