A humble disclaimer often found on technical blog posts. 多分に ('abundantly, to a considerable extent') is slightly literary — distinct from the homophonic adverb 多分 ('probably'). お断りしておく ('to disclaim in advance, to give advance notice') is a polite set phrase combining the honorific prefix お with 断る ('decline, warn') + ~ておく (preparatory). ~ておきます is the polite form of ~ておく.