With my Server-Installation of unofficial (by FRG) en-US SeaMonkey 2.50a1 (NT 6.1; WOW64; rv:53.0) Gecko/20100101 Firefox/53.0 Build 20161211141438 (Default Classic Theme) on German WIN7 64bit I observe some problems with Send-Later-Addon. First my suspect was that there only is a problem that time shift sent emails will not become copied into Sent Folder; works fine if I use [Send Now] for sending immediately. But the problem seems to be more serious, today all my time shift test emails did not reach sender, they are lost. Currently I can’t tell whether the problem only affects time shift sending or whether there is a deeper problem in the send process.
I did my tests only with a POP3 email account.
As long as there is no real knowledge concerning the circumstances I recommend not to use those latest Trunk builds for sending (important) Emails.