It seems that eBay is having a technical issue right now in sending emails but they also have a 5 email limit per day.
If you haven't seen the "you exceeded blah blah.." error message then it seems that your account is affected by the bug. Here's how you can contact another eBay member
1 log in to your account and then click the advanced search link locate on the upper most part of the ebay page next to the search button.
2. then click the link find a member under members on the left side
3. enter the user of the other member (not your user id) and then enter the verificaiton code and hit search.
4 you will then see exact results, click the number of feedback next to the user id in the exact match.
5.you will then see the feedback profile page of the member and then scroll to the right and then click contact member
6. on the next page, click the box for this is not for an item and click continue.
7. you will then see the contact box that you can use to contact the member.
if error still persists, contact ebay.
I hope this helps. Have a great day!