印刷物には、特別郵袋印刷物というのがあります。

、。

Among printed matter, there is what's called 'special mailbag printed matter.'

Literal

Printed-matter [to-には], special-mailbag-printed-matter [called-という] [nominalizer-の] [subject-が] exists.

Dry postal terminology. 特別郵袋印刷物 is a four-compound technical term: 特別 'special' + 郵袋 'mailbag' + 印刷物 'printed matter.' The construction ~というのがあります ('there is what's called X') introduces a term the reader may not know. This is textbook informational prose at its most utilitarian.