By applying some registry fixes I’ve been able to resolve this. The following, when saved to a registry file, then merged, followed by a reboot - should allow the mailto to be changed, eM set as the default Windoze mail client, and also allow for setting the mail handler in browsers such as Firefox.
No guarantees as I’m not certified anything - but this worked for me. I think.
If your installation is somewhere other than “C:\Program Files (x86)\em Client” adjust accordingly.
Windows Registry Editor Version 5.00
[HKEY_CLASSES_ROOT\mailto]
@=“URL:MailTo Protocol”
“URL Protocol”=""
[HKEY_CLASSES_ROOT\mailto\shell\open\command]
@="“C:\Program Files (x86)\em Client\MailClient.exe” /mailurl “%1”
[HKEY_CLASSES_ROOT\em Client.Mailto]
@=“URL:MailTo Protocol”
“URL Protocol”=""
[HKEY_CLASSES_ROOT\em Client.Mailto\shell\open\command]
@="“C:\Program Files (x86)\em Client\MailClient.exe” /mailurl “%1”
[HKEY_LOCAL_MACHINE\SOFTWARE\Classes\em Client.Mailto]
@=“URL:MailTo Protocol”
“URL Protocol”=""
[HKEY_LOCAL_MACHINE\SOFTWARE\Classes\em Client.Mailto\shell\open\command]
@="“C:\Program Files (x86)\em Client\MailClient.exe” /mailurl “%1”
[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\em Client\MailClient\Capabilities\UrlAssociations]
“mailto”=“eM Client.Mailto”
[HKEY_LOCAL_MACHINE\SOFTWARE\RegisteredApplications]
“MailClient”=“SOFTWARE\Wow6432Node\em Client\MailClient\Capabilities”