I've been getting these 2 consistently with clamwin-090.2.1 and 0.91.1 also. I don't detect them with Avast at all.

1. Are they false positives?
2. If not, How can I remove them?

The mailbox is too large to send to virustotal.com for multiple scanner tests.

Scan Started Wed Jul 25 07:51:06 2007
-------------------------------------------------------------------------------

C:\Documents and Settings\Bradley\Application Data\Thunderbird\Profiles\qvvodt1t.Brad\Mail\mail.comcast.net\Inbox: Not deleting/moving mailbox
C:\Documents and Settings\Bradley\Application Data\Thunderbird\Profiles\qvvodt1t.Brad\Mail\mail.comcast.net\_bs_mail: Not deleting/moving mailbox

C:\Documents and Settings\Bradley\Application Data\Thunderbird\Profiles\qvvodt1t.Brad\Mail\mail.comcast.net\Inbox: Email.E-card FOUND
C:\Documents and Settings\Bradley\Application Data\Thunderbird\Profiles\qvvodt1t.Brad\Mail\mail.comcast.net\_bs_mail: Email.Phishing.RB-1309 FOUND
----------- SCAN SUMMARY -----------
Known viruses: 140254
Engine version: 0.91.1
Scanned directories: 50
Scanned files: 171
Skipped non-executable files: 0
Infected files: 2

Data scanned: 231.02 MB
Time: 40.407 sec (0 m 40 s)
--------------------------------------
Completed
--------------------------------------

Sincerely,

bradpskiff

they are likely to be false positives or harmless. you may add the whole mail to the exclusion list, keeping the <> marks to tell it is a regular expression
<C:\\Documents and Settings\\Bradley\\Application Data\\Thunderbird\\Profiles\\qvvodt1t\.Brad\\Mail\\.*>

SDF file extension, "Email.E-Card" (Clam AntiVirus) ....

The one below is what Clam found as the 'Email.E-Card' threat and is a false positive apparently. (MSN subscriber since 2001).

Extension: SDF (Search Results)
MSN Local Machine Mail Storage File (Microsoft)
https://filext.com/file-extension/sdf

"If you have the account abc@msn.com this file will usually be named ABC-MSN-COM.SDF and is typically located in C:\DOCUMENTS AND SETTINGS\\LOCAL SETTINGS\APPLICATION DATA\MICROSOFT\MSN\DB.
.....
This is record 16328 last modified on 2004-04-06."