Crowded "From" field

Crowded "From" field

So how do I get rid of aliases in the "From" field that I never use?  Apart from the primary email my email account has approximately 20 aliases, but I only send email from 4-5 of those while others are only used to receive email. 

When I go to Settings -> Personalize -> Send mail as - I can see the list of addresses and edit them, but I cannot delete them. Is it at all possible? 

I remember that I actually managed to do so a year ago or so. 

Thanks.   

BTW, your Zoho Mail app for iPhone is great! Thank you for rolling it out.