A single trackback ping failure generates a log of logs, at WARN level:

May 6, 2005 5:34:11 PM org.apache.commons.httpclient.HttpMethodBase checkValidRedirect
WARNING: Error getting URI host
org.apache.commons.httpclient.HttpException: Redirect from host tinyurl.com to forwarding.tinyurl.com is not supported
at org.apache.commons.httpclient.HttpMethodBase.checkValidRedirect(HttpMethodBase.java:1192)
at org.apache.commons.httpclient.HttpMethodBase.processRedirectResponse(HttpMethodBase.java:1143)
at org.apache.commons.httpclient.HttpMethodBase.isRetryNeeded(HttpMethodBase.java:934)
at org.apache.commons.httpclient.HttpMethodBase.execute(HttpMethodBase.java:1049)
at org.apache.commons.httpclient.HttpClient.executeMethod(HttpClient.java:638)
at org.apache.commons.httpclient.HttpClient.executeMethod(HttpClient.java:500)
at com.atlassian.trackback.TrackbackUtils.getUrlContent(TrackbackUtils.java:140)
at com.atlassian.trackback.DefaultTrackbackFinder.findPingUrls(DefaultTrackbackFinder.java:49)
at com.atlassian.trackback.DefaultTrackbackFinder.findPingUrls(DefaultTrackbackFinder.java:23)
at com.atlassian.trackback.DefaultTrackbackHelper.pingTrackbacksInContent(DefaultTrackbackHelper.java:27)
at com.atlassian.jira.trackback.TrackbackMailQueueItem.send(TrackbackMailQueueItem.java:61)
at com.atlassian.mail.queue.MailQueueImpl.sendBuffer(MailQueueImpl.java:55)
at com.atlassian.jira.service.services.mail.MailQueueService.run(MailQueueService.java:23)
at com.atlassian.jira.service.JiraServiceContainer.run(JiraServiceContainer.java:53)
at com.atlassian.jira.service.ServiceRunner.execute(ServiceRunner.java:50)
at org.quartz.core.JobRunShell.run(JobRunShell.java:147)
at org.quartz.simpl.SimpleThreadPool$WorkerThread.run(SimpleThreadPool.java:387)
May 6, 2005 5:34:11 PM org.apache.commons.httpclient.HttpMethodBase processRedirectResponse
WARNING: Invalid Redirect URI from: http://tinyurl.com:80/cej2y to: http://forwarding.tinyurl.com/redirect.php?num=cej2y

Generally the failure of a trackback ping is irrelevant to the JIRA admin, and there is not much that can be done in the case of failures, so it should be logged at INFO level.