This is the mail system at host relay.mailchannels.net.
I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.
For further assistance, please send mail to postmaster.
If you do so, please include this problem report. You can
delete your own text from the attached returned message.
The mail system
<shishirkundu68@gmail.com>: host gmail-smtp-in.l.google.com[192.178.163.27]
said: 550-5.1.1 The email account that you tried to reach does not exist.
Please try 550-5.1.1 double-checking the recipient's email address for
typos or 550-5.1.1 unnecessary spaces. For more information, go to 550
5.1.1 https://support.google.com/mail/?p=NoSuchUser
41be03b00d2f7-c1e79c13517si25941163a12.102 - gsmtp (in reply to RCPT TO
command)