在特定情况下，当我通过 thunderbird 发送电子邮件时，该邮件到达时没有 DKIM 密钥，并在源头被标识为垃圾邮件：
X-Virus-Scanned: amavisd-new at mailserver.example.com
X-Spam-Flag: YES
X-Spam-Score: 5.591
X-Spam-Level: *****
X-Spam-Status: Yes, score=5.591 tagged_above=1 required=4.5 tests=[ALL_TRUSTED=-1, DC_GIF_UNO_LARGO=1.323, HTML_IMAGE_ONLY_04=0.342, HTML_MESSAGE=0.001, MPART_ALT_DIFF=0.724, SB_GIF_AND_NO_URIS=2.199, TO_NO_BRKTS_HTML_IMG=2, TVD_SPACE_RATIO=0.001, URIBL_BLOCKED=0.001] autolearn=no autolearn_force=no
在日志中它看起来像这样：
Sep 10 17:02:15 mailserver amavis[10085]: (10085-20) Passed SPAMMY {RelayedTaggedInternal}, ORIGINATING LOCAL [179.179.39.20]:51328 [179.179.39.20] <[email protected]> -> <[email protected]>, Queue-ID: 651981536, Message-ID: <[email protected]>, mail_id: WnptjhExD5Me, Hits: 5.591, size: 21343, queued_as: A77831540, 487 ms
如果我通过与服务器位于同一网络和其他网络上的网络邮件发送，则邮件将带有 DKIM 密钥，并且源中不带有垃圾邮件标签。
在日志中它看起来像这样：
Sep 10 14:37:33 mailserver amavis[10085]: (10085-03) Passed CLEAN {RelayedInternal}, ORIGINATING/MYNETS LOCAL [10.99.0.10]:40774 <[email protected]> -> <[email protected]>, Queue-ID: 18EEA1251, Message-ID: <[email protected]>, mail_id: YsTVvEBEP7SG, Hits: -0.999, size: 1212, queued_as: A31801540, dkim_new=default:mydomain.com, 516 ms
Sep 10 14:37:33 mailserver postfix/smtp[13458]: 18EEA1251: to=<[email protected]>, relay=127.0.0.1[127.0.0.1]:10026, delay=0.62, delays=0.09/0.01/0.01/0.51, dsn=2.0.0, status=sent (250 2.0.0 from MTA(smtp:[127.0.0.1]:10027): 250 2.0.0 Ok: queued as A31801540)
这可能是什么原因造成的？