What all email accounts do we have at the moment who are operating on SHA-1?
No idea about that. Most (all?) E-mail providers require SSL/TLS these days. For example, I am not able to access the POP3 servers of Microsoft without TLS.
Symantec and Comodo still offer SHA-1 certificates (when asked directly) and if your E-mail provider was clever enough, his old SHA-1 certificate is still valid. However, I am not aware of any such provider. You could setup your own server and redirect/forward your your E-mail to that.
Consequently: If you find an E-mail provider which does not require TLS, you avoid this SHA issue (but showing your E-mail content to everyone around you). Alternatively, you try the Web interface of your E-mail provider. Again, many force forward you to HTTPs then, again with this SHA issues.