On your update question:
If all you want is to limit mails/second and you know how many hosts are doing the sending, you might as well throttle each host to 1/hosts of the rate one host would be sending.
So 2 hosts would be sending at 1/2 of the rate one host sends. No communication necessary for that

if you really really want communication, then the database all the hosts are already accessing gives a convenient means to coordinate.
For example it could give out contingents of email adresses to each host that are put in by one coordinator process at the specified rate.

Perl threads could be used similary, one coordinator thread and many sub-threads. Counter question: Safe from what?

---

---

• Are you posting in the right place? Check out Where do I post X? to know for sure.
• Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:

  <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>

• Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
• Want more info? How to link or How to display code and escape characters are good places to start.