Here were some that we thought of before:

Whom did X email within some date range

If X and Y are involved then who is in common that they both
emailed with before a certain date.

Has X sent email to more than 10 people in any 4 hour interval?

How many people have sent emails to X in these six hours?

Is there a sequence of emails linking X to Y such that the sequence
is ordered in time, e.g. X sent to A on day 1, A sent to B on day 2, .... Z sent to X on day 25.

What if that sequence cannot be more than k long?

What if the interval between messages in that sequence must be at least one hour but no more than one day?

Find the list of everyone who transitively sent to X (either
directly to X or through intermediaries)  over the last four days?


Among this set of people  which pairs have communicated the most
over the last three days?

Define a session as an email exchange between X and Y such that there
is a communication from X to Y or from Y to X every day or more frequently.
How many sessions are there between X and Y in the last month.


A set of known lawyers.
A set of other people who at one point met the lawyers.

Are there any pair of people P1 and P2  that have both
used this lawyer and that bank
in the past and such that P1 and P2 later exchanged emails?