Typically within 1 to 2 hours; in some case it might take a full day. The primary reason for the delay is that any change to your domain's "MX" records do not take effect immediately, but must propagate through the Internet. Technically, your MX records have a "TTL" (Time-To-Live) value which specifies how quickly changes will take effect. A typical TTL value is 12 hours, but your domain may be configured with another value, such as 24 hours. Because some DNS servers don't honor the TTL, it can take up to 72 hours for the majority of your email to start passing through our service.