Hauthafrong54 Do you mean a mail which you deleted or an e-mail account you deleted?
For the first case, take a look in the trash folder "dustbin", if the mail is there, you can draw it back into a mail folder of your choice, if it is no more there, it is probably deleted permanently and you have no chance to retrieve it.
For the second case, take a look in MySwisscom > Home > More > Email:
Direct link: https://www.swisscom.ch/myswisscom/d?useCase=viewMailHub
If you're account has not been deleted more than 180 days ago, you will find it there and then you can reactivate it, if it is longer ago, it is over, no chance to retrieve it.