© 2017 Wolters Kluwer Health, Inc. All rights reserved. Background: Physician e-mail communication, with patients and other providers, is one of the cornerstones of effective care coordination but varies significantly across physicians. A physician's external environment may contribute to such variations by enabling or constraining a physician's ability to adopt innovations such as health information technology (HIT) that can be used to support e-mail communication. Purpose: The aim of the study was to examine whether the relationship of the external environment and physician e-mail communication with patients and other providers is mediated by the practice's HIT availability. Methodology: The data were obtained from the Health Tracking Physician Survey (2008) and the Area Resource File (2008). Cross-sectional multivariable subgroup path analysis was used to investigate the mediating role of HIT availability across 2,850 U.S. physicians. Findings: Solo physicians' perceptions about malpractice were associated with 0.97 lower odds (p <.05) of e-mail communication with patients and other providers, as compared to group and hospital practices, even when mediated by HIT availability. Subgroup analyses indicated that different types of practices are responsive to the different dimensions of the external environment. Specifically, solo practitioners were more responsive to the availability of resources in their environment, with per capita income associated with lower likelihood of physician e-mail communication (OR = 0.99, p <.01). In contrast, physicians working in the group practices were more responsive to the complexity of their environment, with a physician's perception of practicing in environments with higher malpractice risks associated with greater information technology availability, which in turn was associated with a greater likelihood of communicating via e-mail with patients (OR = 1.02, p <.05) and other physicians (OR = 1.03, p <.001). Practical Applications: The association between physician e-mail communication and the external environment is mediated by the practice's HIT availability. Efforts to improve physician e-mail communication and HIT adoption may need to reflect the varied perceptions of different types of practices.