Complex sentence: Trouten's mother received several typed letters, purportedly mailed while the couple was abroad, although the envelopes were stamped with Kansas City postmarks, and the letters were, her mother said, uncharacteristically mistake-free.
Split into simpler sentences: Trouten's mother received several typed letters, purportedly mailed while the couple was abroad, although the envelopes were stamped with Kansas City postmarks. The letters were, her mother said, uncharacteristically mistake-free.