: These are likely unique identifiers, checksums, or encoded strings. In some instances, similar patterns appear in:

: It may be a fragment of a UUEncoded or MIME attachment found in the header of an email. Recommendation

: This string could be a "Stop Code" or a memory address identifier generated during a software crash or hardware failure.

: Specific identifiers used by software to track assets or records. Possible Origins

送信済みMailの文字化け - Apple サポートコミュニティ

: This is the file extension for the 7-Zip compressed format . The presence of "7z" suggests that the string is related to a compressed archive or a segment of one.