It seems like Unix tools could be used to chop this up fairly effectively. For example, if you had a single text file with all target addresses in it, one per

It seems like Unix tools could be used to chop this up fairly effectively. For example, if you had a single text file with all target addresses in it, one per line... - "split" could be used to cut the list into chunks (separate files) - delays could be set up in tools such as "at" or "crontab", so that E-mails of each sub-file are attempted at entirely different times (e.g. an hour apart) - a script written in shell or almost anything else could iterate over a given file's addresses and send messages