I could mail you could mail he could mail we could mail you could mail they could mail
V-ing form
I could be mailing you could be mailing he could be mailing we could be mailing you could be mailing they could be mailing
Perfect
I could have mailed you could have mailed he could have mailed we could have mailed you could have mailed they could have mailed
V-ing perfect
I could have been mailing you could have been mailing he could have been mailing we could have been mailing you could have been mailing they could have been mailing
Negation
Simple form
I could not mail you could not mail he could not mail we could not mail you could not mail they could not mail
V-ing form
I could not be mailing you could not be mailing he could not be mailing we could not be mailing you could not be mailing they could not be mailing
Perfect
I could not have mailed you could not have mailed he could not have mailed we could not have mailed you could not have mailed they could not have mailed
V-ing perfect
I could not have been mailing you could not have been mailing he could not have been mailing we could not have been mailing you could not have been mailing they could not have been mailing
Interrogative form
Simple form
could I mail? could you mail? could he mail? could we mail? could you mail? could they mail?
V-ing form
could I be mailing? could you be mailing? could he be mailing? could we be mailing? could you be mailing? could they be mailing?
Perfect
could I have mailed? could you have mailed? could he have mailed? could we have mailed? could you have mailed? could they have mailed?
V-ing perfect
could I have been mailing? could you have been mailing? could he have been mailing? could we have been mailing? could you have been mailing? could they have been mailing?
Interro-negative form
Simple form
could I not mail? could you not mail? could he not mail? could we not mail? could you not mail? could they not mail?
V-ing form
could I not be mailing? could you not be mailing? could he not be mailing? could we not be mailing? could you not be mailing? could they not be mailing?
Perfect
could I not have mailed? could you not have mailed? could he not have mailed? could we not have mailed? could you not have mailed? could they not have mailed?
V-ing perfect
could I not have been mailing? could you not have been mailing? could he not have been mailing? could we not have been mailing? could you not have been mailing? could they not have been mailing?