Yes, you can use the email address of his representative and also u can use one email id for multiple returns....

senior citizen means the elder family members who has family members also, so he can use the mail id of his family member for e filing, 

email id is needed by department to send the ITRV, reset of passwords, transmission of assessment orders, and communication between department and assessee, so for safeside its not wise to provide the third party email id to department, as important communications may get missed in case of 3rd party ids.

Yes Its possible. I as a accountant, use only one official id which I is specialy created for E-ITR. There is no harm in it sincedepartment wants mail id only for sending communication. So, you can use same mail id for all type income of incometax returns (Individual, HUF, AOP, BOI, Co. etc) but Always remember that E-filling is not available for TRUST or Society (ITR-7).

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