Hi Mieke,

As far as I know, the only way is via a SLNet message.

Here is a snippet that should help you with this

var securityInfo = engine.SendSLNetSingleResponseMessage(new GetInfoMessage(InfoType.SecurityInfo)) as GetUserInfoResponseMessage;
Dictionary<string, string> emails = new Dictionary<string, string>();
foreach (var user in securityInfo.Users)
{
emails.Add(user.FullName, user.EmailAdress);
}

If you do not need all email addresses you can replace the dictionary and the emails.Add with a simple filter, like below

var email = securityInfo?.Users?.FirstOrDefault(user => user.FullName == engine.UserDisplayName)?.EmailAdress;