Normally sending letters and asking for work from other CA firms is not a misconduct but we cannot misuse this exception, like the firm did here.
Here  CA M more than asking for work was advertising himself to another firm by mentioning things that can be influential.
 
Sending letters is principally covered in clause 6, clarifications and permissions are also given in clause 6. So even if professional attainments are highlighted (generally covered by Clause 7 )court has applied clause 6.
 I understand that it includes highlighting professional matters. But in PE more than interpretation we have to understand pattern.