A non-transitory computer-readable storage medium may comprise instructions stored thereon. When executed by at least one processor, the instructions may be configured to cause a server computing system to at least maintain electronic messages received by a user, at least one of the electronic messages including textual content and a Uniform Resource Locator (URL), retrieve, more than once, a file identified by the URL from a remote server identified by the URL, subsequent to each retrieval, determine whether content of the file identified by the URL meets a trigger condition, and based on determining that the file identified by the URL meets the trigger condition, cause a client computing system associated with the user to modify a presentation of the at least one electronic message that includes the textual content and the URL.