Bulk SMS can be an effective way to thank your donors and supporters during special occasions like holidays or anniversaries. Here are the steps to follow:

1. Collect phone numbers: First, you need to collect the phone numbers of your donors and supporters who you want to thank. Make sure you have their permission to contact them via SMS.
2. Choose a bulk SMS service: There are several bulk SMS services available online. Choose one that fits your needs and budget.
3. Compose your message: Keep your message brief and to the point. Start by expressing your gratitude and thanking your donors and supporters for their contributions to your charity. Then, wish them a happy holiday or anniversary and express your hope for their continued support.
4. Personalize your message: Address your donors and supporters by their name in the message. This will make them feel more connected to your charity.
5. Include a call-to-action: Include a call-to-action in your message, such as “Thank you for your support. Please continue to support our cause” or “We appreciate your contributions. Please spread the word about our charity to your friends and family.”
6. Schedule your message: Choose a date and time when it’s appropriate to send the message, such as during the holiday season or on the anniversary of your charity’s founding.
7. Send the message: Once you have composed and scheduled your message, send it to your donors and supporters.
8. Follow up: Follow up with donors and supporters who reply to the message. Thank them for their continued support and encourage them to stay engaged with your charity.
   Remember to respect your supporters’ privacy and preferences. If they opt-out of receiving SMS messages, make sure you remove their phone number from your list. Also, avoid sending too many messages as it may lead to supporters feeling overwhelmed and opting-out.