Sending emails successfully involves several factors, including IP reputations, back-end infrastructure, whitelisting, feedback loops, bounce handling, and content. A good IP reputation is crucial for getting to the inbox, with factors such as volume, spam complaints, engagement, and content type influencing it. Setting up a mail server properly, using an external service like Return Path, and being mindful of ISP requirements are also important. Additionally, whitelisting, feedback loops, and proper bounce handling can help prevent delivery problems. However, the sender's responsibility is also crucial, as content that may be perceived as spammy or misleading can block emails. Understanding what types of content to avoid and how to provide clear and concise information is key to success in email sending.