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If you take a look at the timestamps from this type of consolidated emails, you would notice that daily consolidated emails from Linkedin and Yahoo! Groups usually come at around the same time every day. This is most likely true for all such services since they are sent automatically on a regular schedule.
Being the top post for this type of email has many benefits. Obviously, the top 2 or 3 posts get the most attention. In addition, for LinkedIn, see the example in the figure (click the image to see the larger version), you will see that the poster name for the first post even appear in the subject line!
If we are building awareness and traffic using newsgroups in popular and high volume newsgroups, the trick is to time your posting so your post appears on the top. The exact method is slightly different for different services.
For example, for linkedin, the latest post appears on the top, and the rest are listed in reverse chronological order, therefore, you would want to time your posting right before the email deployment time.
On the other hand, for Yahoo! Group, posts are listed chronologically for the day before. So if you post at 12:01am on Monday (make sure you take into account the time zone!), you will be the top message for Tuesday.
Try it out, experiment, and let me know how this works out for you!