AT&T's email filtering and infrastructure are a combination of in-house processes and outsourced services, primarily to Yahoo/VMG. While AT&T manages some aspects, like initial server connections and the Mail Transfer Agent (MTA) in some instances, a significant portion, including the Mail User Agent (MUA) and filtering for residential accounts and legacy domains (e.g., pacbell.net), is handled by Yahoo/VMG. AT&T also employs standard security measures such as SPF, DKIM, and DMARC and its network reputation is monitored by organizations like Spamhaus. Due to potentially aggressive spam filtering, legitimate emails may be blocked. Troubleshooting often involves checking spam folders and contacting AT&T or Yahoo support, depending on the domain and the specific issue. Peering agreements also affect deliverability.