In this work, a receiver architecture for the detention of on-off-keying (OOK) signals using adaptive signal estimation and threshold setting for free-space optical communications is investigated. It is assumed that the received signal is impaired by channel fading, modeled using Málaga (M) distribution, and an imperfect pointing acquisition. In OOK communications, knowledge of the received signal is required to set the optimum receiver threshold. To that end, a linear estimation technique is utilized to estimate the combined impact of the residual pointing error and channel fading. The performance of the resulting receiver is evaluated and is compared with those of a receiver in which the channel and pointing impairments are ignored and with a receiver in which the channel and pointing impacts are replaced by the statistical averages of those impairments. It is shown that, for reasonable system parameters, the proposed receiver offers a significant improvement in performance in terms of the overall bit error rate (BER) when compared with its alternatives. For a scenario in which a significant pointing error is present, it is observed that channel estimation does not offer a benefit in terms of the overall BER.