Main Street Capital Corporation (NYSE: MAIN) completed a follow-on investment of $15.6 million in UBM ParentCo, LLC, which operates as United Business Mail, according to a company statement. The investment supports UBM's strategic acquisition of a national provider of mail consolidation and freight brokerage services.

Main Street made the investment alongside MSC Income Fund, Inc. (NYSE: MSIF). The funding consists of first lien, senior secured term debt. Main Street and MSIF initially invested in UBM in December 2025.

UBM, founded in 1987 and headquartered in Chicago, provides marketing mail commingle services and logistics optimization for large-scale mailers. The company acquired Mystic Logistics, a mail consolidation and freight brokerage company, in December 2025 to expand its transportation capabilities.

The acquisition target provides asset-light palletized mail consolidation, mail optimization services, freight brokerage, and warehousing and distribution for business-to-business and business-to-consumer customers.

Main Street Capital is a principal investment firm that provides debt and equity capital to lower middle market companies. The firm's portfolio companies typically have annual revenues between $10 million and $150 million for its lower middle market strategy and between $25 million and $500 million for its private loan strategy.

MSIF focuses on providing debt capital to private companies owned by or being acquired by private equity funds. The fund's portfolio companies generally have similar revenue ranges to Main Street's investment strategies.