The command-line option you are looking for exists. I found out by decompiling MailClient.dll and searching for the JumpList-entries.
Creating a shortcut with this parameter will always open calendar-view:
“C:\Program Files (x86)\eM Client\MailClient.exe” /newmainform_calendar
Alternatively reroute over cmd, then you can have more than one shortcut to eM-Client in taskbar:
C:\Windows\System32\cmd.exe /c start “” “C:\Program Files (x86)\eM Client\MailClient.exe” /newmainform_calendar
For documentation, this are all the parameters I found in MailClient.dll:
/newmail
/newcontact
/newevent
/newtask
/newnote
/newmainform_mail
/newmainform_calendar
/newmainform_contact
/newmainform_task
/newmainform_attachment
/newmainform_note
Additionally in registry you can find the following parameters:
"C:\Program Files (x86)\eM Client\MailClient.exe" /open "%1"
"C:\Program Files (x86)\eM Client\MailClient.exe" /url "%1"
"C:\Program Files (x86)\eM Client\MailClient.exe" /mailurl "%1"
"C:\Program Files (x86)\eM Client\MailClient.exe" /subscribe "%1"
"C:\Program Files (x86)\eM Client\MailClient.exe" "%1"
"C:\Program Files (x86)\eM Client\MailClient.exe" /startup
"C:\Program Files (x86)\eM Client\MailClient.exe" /spadhideicons
"C:\Program Files (x86)\eM Client\MailClient.exe" /spadreinstall
"C:\Program Files (x86)\eM Client\MailClient.exe" /spadshowicons