Multichannel marketing refers to the act of interacting audience utilizing management for both inbound and outbound advertising programs.
Omnichannel and multichannel marketing approach can can be treated equally. Generally, it means establishing customer-centric communications with your clients by using different channels in addition to your email campaigns, be it web push notifications, mobile push notifications, SMS text messages and other instant messages like Telegram, Viber, Facebook, Instagram etc.
You can read more about multichannel and omnichannel marketing here: https://esputnik.com/en/blog/what-is-omnichannel-marketing
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