ASP.Net Error: The index entry of length 904 bytes for the index exceeds the maximum length of 900 bytes

I am unable to save details with some emailids.I am getting this error "The index entry of length 904 bytes for the index 'IX_companyinfo_exhibition' exceeds the maximum length of 900 bytes." https://ibb.co/k3XP2c

when i entered the following emailsids,its not getting saved:

info@combilift.com marketing@hildaautomation.in info@pakona.com info@himedialabs.com info.lho@liebherr.com

During debugging,in catch block,i found that i got this error "The index entry of length 904 bytes for the index 'IX_companyinfo_exhibition' exceeds the maximum length of 900 bytes."