public ISet <string> ExpandDistributionLists(
string sender,
IEnumerable <string> originalRecipients,
HashSet <string> excludedFromExpansion)
{
var to = new HashSet <string>();
foreach (string recipient in originalRecipients)
{
DomainSettings domain = null;
if (_domainSettings.TryGetValue(
MailUtilities.GetDomainFromMailbox(recipient),
out Lazy <IVolatile <DomainSettings> > settings))
{
domain = settings.Value.Value;
}
DistributionList distributionList = domain?.DistributionLists?.FirstOrDefault(dl => dl.Mailbox == recipient);
if (distributionList != null)
{
if (!CheckValidSender(sender, distributionList))
{
_log.Warning($"Attempt by invalid sender {sender} to send to DL {distributionList.Mailbox}");
continue;
}
IEnumerable <string> nonExcludedMembers = distributionList.Members.Where(m => !excludedFromExpansion.Contains(m));
foreach (string member in nonExcludedMembers)
{
to.Add(member);
}
continue;
}
{
// C# compiler mistake that prevents collapsing the domain.Alias null check
if (domain?.Aliases != null && domain.Aliases.TryGetValue(recipient, out string newRecipient))
{
if (excludedFromExpansion.Contains(newRecipient))
{
continue;
}
to.Add(newRecipient);
continue;
}
}
to.Add(recipient);
}
return(to);
}
public static bool CheckValidSender(string sender, DistributionList distributionList)
{
if (!distributionList.Enabled)
{
return(false);
}
if (!distributionList.AllowExternalSenders &&
MailUtilities.GetDomainFromMailbox(sender) != MailUtilities.GetDomainFromMailbox(distributionList.Mailbox))
{
return(false);
}
return(true);
}